OMG. And, you go "look at" the weblink I posted to Washington DC Thai Embassy. Either way, you were in fact wrong when you said money in Thai Bank Deposit, does not earn interest (in fact it compares very favorably with Banks outside of Thailand, sometimes higher). And, as you admitted, requires Thai Health Insurance, which is not inexpensive.
You are way Wrong. Deposit in the Thai Bank DOES earn Interest (and usually better rate than home country, at least USA). Also, O-X Visa DOES require Deposit in Thai Bank, and much more than normal Non-O (or even O-A), specifically 3 MIL. Baht, AND, also requires maintaining Health Insurance for entire duration of stay (10 years), AND, further requires Medical Check/Certificate and Criminal Check; AND $400 Visa Fee. No thank you.
Your last comment "... but with visa-exempt entry, airlines have nothing to check" is Wrong. They can, and most will, check on your proof of departure flight and deny you boarding if you don't have. But, one option, is to book fully refundable Ticket and then cancel after arrival.
If you don't want to put the 800k in Thai Bank then Retirement Stay is not an option for you -- at least 1st year. But, if you plan ahead, an acceptable alternative is to deposit monthly pension monies of 65K per month into Thai Bank, for 12 months. (Or, if you have the money, you can still deposit the 800K 1st time, then begin the 12 monthly deposits so by 2nd year renewal, you can do it that way, and withdraw your 800k). Again, let me know if you want instructions for getting your Retirement Stay using the 800k method (in-country).
It would be helpful to know the Nationality of the Passport you are traveling under. If you are from one of the Visa Exempt countries, and will be arriving before April 1, you will already get free 45-day Entry Stamp upon arrival. And, then, you if you need additional time, you can extend that another 30 days with TM7 Application at local Immig. Office. So, really no need for Tourist Visa at this time (if, you are Visa Exempt).
While checking into "cheap hotel" is certainly an option. Not really necessary. You can either go in person to local Immig. Office and register TM30. Or, now there is a TM30 App., that is easy to use; and, you can self-register.