First, the borders are closed, and it's unknown when they would reopen.
>now I have been told that I can get a straight NON O 90 day visa each time....
I don't think you can. According to
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-Non-Immigrant-visas.html#6,
You need 10,000 British Pounds before they issue you that Non-O visa in a bank account.
> I plan to spend three months at a time having to come home to renew the visa each time
Acquiring single entry tourist visas to live in Thailand is a *VERY BAD* plan. Having a visa is no promise that you will be allowed entry. IF you are denied entry by air, you will have to stay at an immigration detention center UNTIL you can buy the next flight home. I've seen pictures of these centers, they don't look nice at all.