My Thai wife also signed our condo lease. Six years and no one ever asked to see the lease. I kept bringing it with me to immigration but they never asked.
You will have to show you meet the financial requirements each year that you extend your O visa. They will ask for bank statements and your bank book. There will be several non financial documents to submit as well.
After 90 days you extend the O visa for 1 year and you state on the extension form that the reason is "retirement". This will determine the financial and other requirement you must meet to get the extension. You can extend year after year indefinitely. Note that the OA visa also expires eventually and it also can be extended yearly.
There is a lot that is not clear to me. Either talk to a tax professional or wait and see what happens when people start filing in January. I have a pensioner LTR so the money I bring into Thailand is not taxable. I don’t have skin in the game.
My strategy is to have a high deductible. Self insure for routine health care. Keep the insurance for a catastrophic health event. I have a 40,000 baht deductible and, in 7+ years, have never had a medical bill greater than 20,000 baht, usually much lower.
If you are asking about short term travers health insurance then I don’t know.
Paying up front will reduce the number of attempts to find out what will work. It's just going to take longer to interpret the soft power stuff and we will continue to get these questions.
I have an LTR. I was just curious about this visa but I am going to be scrolling a lot if I follow it at all now.