You’re mistaken. Please go on YouTube to see healthcare options in Thailand.
I figure you likely know this, but Chang Mai is a hub for western missionaries operating throughout SE Asia, with a lot of organizations having operations there, Bible translation work into many tribal languages and so forth. That’s probably a significant part of the expatriate community there.
Older western men usually like Thailand more than western women, because they are treated better by the locals. Of the few retired western couples around, the wives tend to look sour and unhappy. Solo western men have a much better go of it, especially if they meet a local Thai woman to help them navigate the country.
Once someone has enough wealth to support their needs, relative wealth compared to their neighbors leads to more happiness than having more money. In the USA, an older man might be in the top 20% of wealth, but be practically invisible in public. Overnight, that very same man living in Thailand is in the top 1%, and noticed everywhere they go. There are many variables, but for some, Thailand turns out to be the happiest place they've ever lived. If you have some money, it's worth a try! If you are poor, Thailand is probably not your best option.
If you like going to restaurants and having shopping options, Bangkok is the place to be. Downtown is too busy, but being 30 minutes taxi to the east, towards the big airport, might be just right. It is not necessary or desirable to own a car unless you live farther into the suburbs.