I recommend that a Retirement Visa is the best for you and that you should obtain it from the Thai Embassy/consulate in your country prior to coming to Thailand. I say that because if you come to Thailand on a Visa Exempt stamp or tourist visa, then you will be unable to open a bank account in Thailand and a Thai bank is required to obtain such a visa while in Thailand.
I am 78 years old and have lived in Chiang Mai for over ten years. I chose Chiang Mai because I have a number of serious medical conditions and because the medical (GP, specialists and hospitals) support here is excellent and, in my view, affordable. As an example I can usually obtain walk in appointmets to my heart and diabetes specialists in excellent private hospitals about 1,000 thb, which is cheaper than seeing a GP in my country. The smokey season has not been a problem for my family. Last year was a good year with not much problem and the Thai Government has promised to fix the smoke pollution problem. We do however, have an air filter machine for each of our bedrooms and another for the lounge/living area.
Most countrys and reasonalby minded people accept that up 90 days in a country is tourism. A good example of this is the international agreement that allows tourist to drive on their national licence (often also requires an International Drivers certificate) in a cnother country as a visitor - universally accepted as 90 days. After that visitors need to obtain a licence from the country (as in Thailand). After 90 day in a country being visited, a person is no longer consider a tourist.
It will always be up to the Immigration Officer who takes your passport when you arrive, Having said that, your past history of staying in Thailand indicates that you are not a tourist anymoe but are trying to stay longer term in Thailand. Therefore, if you attempt to arrive on a Visa Exempt Stamp, then you are lokely to be taken aside for questioning and possibly refused entry into Thailand. Best you obtain a visa appropriate to the reason for your stay in Thailand.