Congratulations on your retirement. Do explore FB groups such as U.K. citizen's rights beyond Brexit. It's absolutely wonderful. You have to apply to be a member. Once you're in you'll find a lot of info on the hyperlink and you can also post specific questions.
Healthcare in Italy it's a postcode lottery a bit like in the U.K. Private healthcare is very good and cheaper than in the U.K. but with your existing condition it would be expensive.
I live in Tuscany and I'm very happy with my choice of town (I live near Volterra, Pisa province). You ought to look at small towns or villages with easy access to larger cities especially if you want to avoid apartment living. I would stick with the Pisa or Siena or Lucca provinces. Not to say other cities in Tuscany aren't great but I found some to be rather isolated and isolating. Volterra for instance is very car oriented as public transport is lacking. Do consider the weather and how the hot summers would affect you. We don't have the same weather in Italy we had 30 years ago. The four seasons are no longer as climate change is in full swing. Personally I've chosen a place at almost 500 mt above sea level as I cannot stand the increasingly sweltering summers we are experiencing in this part of Europe. We do have mosquitos and gnats but not as bad as in some places. . I'm only an hour from Pisa and yet I find summers are way too hot in Pisa or Siena and winters a lot damper in Lucca for instance... Climate can change even within relatively small areas. I also deliberately avoided very touristy places as they're totally dead in winter and offer very little to long term residents. Like you I made sure I was near a decent hospital. In Tuscany healthcare is normally good. I also wanted somewhere with a fairly large international presence as my husband's Italian is fairly poor and learning after a certain age isn't easy.
Do visit several places, Italy is fairly big and really varied. Bureaucracy is a real pain, do not underestimate this. It's mind boggling at times! Getting to know locals can also sometimes be a problem.
Do your research and with a bit of luck you can find the right place to retire to. Your combined monthly income should allow you a very comfortable life. Some italian pensioners here live on state pensions of around €700 per month or less. I wouldn't recommend that! Especially as getting older you might need extra help like a gardener or cleaner or (hopefully not!) carer .. and those are expensive!
Last bit of advice: beware estate agents and find a good cross border accountant to help you navigate the complex and expensive fiscal system. Good luck!