The second option is better. non O-A retired requires health insurance. Non-O retired (gotten in Thailand) does not require health insurance. Bring with you all the paperwork you will need including police background check ect. Get a full list of what is needed from the Thai Immigration website.
Best to get a special “Direct Deposit” account and have SS deposit’s your money directly into that account. SS is not taxed in Thailand. But you may have to prove the source.
keep in mind that if you do it as David suggest you will need to get a police report, and health insurance, and a lot of other documents. Life will be much easier to follow Mike’s advise. 60 or 90 day visa to come here then go through the process to get an Non -O retired inside Thailand. (As apposed to the Non-OA you get in your country) again O-A’s require insurance.