@beaconsfieldfarm
In theory, Bulgaria is very similar to the UK in that there's a public health system (like the NHS) and private hospitals and clinics (like BUPA). You can register in the public health system with NAP, and/or you can purchase true private health insurance, just as you could pay BUPA in the UK. The public option is possible by paying contributions as an employee, self-employed, or (in some cases) unemployed. It's also possible with an S1 form given to those receiving a state pension in the UK or EU. There is an online system which hospitals and doctors can use to check if you're fully paid-up, and hence entitled to state care (using your ID number from your residence permit).
The big difference, I feel, is that in the UK they are two separate systems. You can go NHS for free treatment, but it can take you a few months or years (if it's not an emergency) to work through the system. Or, you can elect to go private and get high-cost, but fast treatment. You pay the cost yourself, or via your private insurance policy.
Here, the two seem to be somewhat integrated, in that (most) private hospitals are in (or affiliated with) the public system. And they will receive the standard payment for your operation. And thus you will only pay the "upgrade" price for your private room, gourmet grub, and VIP treatment. As Bulgaria is rather low-cost, these private fees are surprisingly inexpensive. You can choose to pay this upgrade fee yourself, or your private health insurance policy will cover it. Interestingly, if you are covered in the public system (and hence entitled to free or nearly-free care), your private insurance policy will be less expensive (because they know they will only be paying the upgrade cost, not the full private cost).
The other big difference is that the UK NHS has to cope with 10X the population of Bulgaria (nearly 70m vs. nearly 7 million) which means, inevitably, slower response to emergencies, long waits for routine operations, and overloaded GPs.
My personal experience:
I am in the public system (paying the unemployed rate of about 14 euros per month) and hence entitled to public healthcare. They gave me a Bulgarian EHIC too, so that I'm covered when elsewhere in the EU.
I have registered with an English-speaking GP, but finding English speakers can be tricky. He has a daily clinic at Medline, a private hospital. But he's in the public system too. The private consult fee is typically 15-25 euros, maybe higher for some specialists (I paid 50 euros for dermatologist in the same hospital). If you are fully covered in the public system, his fee is 5 euros I think.
I also found an excellent dentist, who speaks near-perfect English. Just like UK, there is very little that he will do on the NHS, pretty much everything is a private option. But the prices are very low.
I am in Plovdiv, the second largest city, so we have several private hospitals, loads of pharmacies, and it's easier to find English-speaking professionals. Veliko Tarnovo is a smaller city, but I'd expect it to have similar facilities. But, of course, you'd have most options in the largest cities Sofia, Plovdiv, Varna, Burgas.
You should note that while I'm in the public system, and entitled to public healthcare, I have not actually used any public hospital. I have been in a couple, and they are nowhere near as busy as UK hospitals, but they are a lot more crowded than private hospitals. Usually, I've used Medline and Pulmed which are very nice private hospitals, and it's very easy. But, in fairness, I've only had consults and diagnostics, rather than actual treatment/operations.
I have been to Medline for the GP, the dermatologist, the orthopedist, and the cardiologist. Minimal waiting, small consult fee. I have walked in to both Medline and Pulmed and asked for a diagnostic (X-ray, MRI). They ask why, and whether it's an emergency (which it wasn't) and then give me an appointment for next day. Good prices (couple of hundred for MRI, 50-odd for X-ray). Blood tests they do on demand. I did once (because feeling too lazy, and had not yet found a GP) just walk over to Pulmed's Emergency Room. I said it wasn't an emergency, but they didn't care. There was 1 person waiting in front of me. They gave me a blood test, quick physical (pulse, blood pressure, bit of prodding me), EKG, and ultrasound. Said I was tip-top and gave me a bill for 60 euros (for emergency doctor consultation and several tests).
Recently, I did a self-check. I got a full blood panel (with cholesterol, hormone levels, and cancer markers, the full monty) at Ramus Labs (walk-in, no waiting, 55 euros). Then I went to the Medline cardiologist and got a full heart check (physical exam + discussion, pulse and blood pressure, heart ultrasound, EKG and echocardiogram). No waiting, was out in less than 45 minutes with my results and report, charge was only 60 euros (including private consult and all the mentioned tests). Then I went to the dermatologist to give me a (nearly) whole-body exam for any suspicious moles/lesions. One person in line, private fee 50 euros as mentioned above.
My dentist is fabulous. He has given me excellent treatment over the last 3 years. He does a thorough cleaning and polishing (about an hour, with the actual dentist, and using the carbonate spray machine to finish) for only 50 euros.
In general, I'm amazed by the quality. My GP and my dentist are better than any NHS option I've had in the UK. And there's rarely any waiting, and they take as long as we need (not rushing me out after 5 minutes like NHS GPs have to do). Even a private hospital in the UK will be very booked and scheduled. Here, I've just rocked-up when I feel like it, and usually get what I want pretty much immediately. The private hospitals are mostly very shiny and new with excellent facilities. And the upgrade prices that I've seen are very low. I might get killed by a bus tomorrow (or a Bulgarian driver, some of them can be pretty wild), but otherwise I have no concerns about the Bulgarian health system keeping me going. :-)
Other Expats:
I don't know lots of expats, unfortunately, so I can't really speak to the experience of others. But we are friends with 3 other expat couples. One couple (Germany + Hong Kong) is living in Plovdiv, and they recently signed up at NAP, based on a German-issued S1. They registered with my GP too, and are very happy with the service at Medline. The 2nd couple (Brit + Brit) is living in a small village just outside Veliko Tarnovo. They said their village doc is great and she speaks English. They have needed a few things, and the doc arranged everything at local public hospitals (usually the same or next day). Very straightforward and they are very happy (and they said the cost is "peanuts"), and so far they have done everything through the public system. The 3rd couple (Bulgarian/Brit + Brit) were the ones that recommended Medline and my GP (as existing patients). They are older, and have required multiple hospitals stays (including emergency treatment). They have free healthcare entitlement based on UK-issued S1s, but they get all treatment at Medline or other private hospitals in Plovdiv. They have paid all upgrade costs from their own pockets, and they are shocked by how cheap it has been. They are delighted with the level of service/treatment, and consider far superior to the quality of care they would have received in the UK on the NHS.
Cost comparison THR (Total Hip Replacement):
For a specific, I can discuss hip replacement operations, as that's a very common surgery for older folks. And thanks to a very hard sporting life and several accidents/injuries, my hip is about as damaged as it can get. I have therefore researched this extensively. One of my Sofia consults (private again, around 50 euros for each one, minimal waiting) said he'd seen better hips on his 80-year old patients. :-)
The UK NHS considers hips non-urgent, so it can take a while, depending on how bad your GP (and your hospital consultant) thinks it is. My dad spent several years until he got his first one. But this is free. I've checked UK private hospitals, and a standard hip implant can be 15k UKP give-or-take.
I searched online, and overseas operations is a thriving market for Brits (due to the long NHS waits). There are low-cost orthopedic (and many other specialities) clinics in Turkey. I also found Nordorthopaedics in Lithuania, who seem to be highly regarded. Their cost for THR package is about 7.5k euros.
In Bulgaria, you can also get a free hip implant in a public hospital. I went for several consults in large private hospitals in Sofia. They said I don't need a referral, and I don't need to go via the public system. They judge my hip to be impaired, so I can have the operation whenever I want (not tomorrow, but next week, say). They said the upgrade price if I have a standard (NHS style) implant would be around 500 euros. I said I wanted the fancy operation (muscle-sparing option) and the fancy implant (top-of-the-line titanium implant with more range of movement ideal for athletes) and an extra week of rehab rather than going straight home. The upgrade price they quoted for this (in a very fancy hospital) was 1,500 euros.
However, I still haven't gone for it. A combination of wanting to see how far you can get with lifestyle changes and non-surgical options... and terror at the thought of hospitals and operations. :-)