The non O in uk doesnt need the police check and is pretty straightforward to get. Cant remember the updated regs now regarding insurance but the extensions in thailand dont require it. The London embassy website is quite good and has all the info if you dig around a little. Getting the extension in thailand is no hassle provided you deposit the 800k in good time.
As James says your alternative is tourist visa and then the non o in thailand. I did mine in the uk.
thanks James ...will look up on the thai embassy website to update myself ...being on an O extension (retirement) hopefully will continue to not be relevant (until the next change? 🙄)
covid insurance yes, everyone currently has to have. The 40k out and 400k in insurance for OA is a significantly heavier burden. Not required for O retirement extension. Better general Medical insurance can be bought overseas rather than in thailand for medical bills. Some may even cover the covid requirement.
The way you are doing it is a quite expensive and complicated way ...extensions in country are usually easier, and can be done by logistics on your foreign trip dates. Arguably a non imm O for 3 months and then extend in thailand yearly due to retirement is cheaper and easier by avoiding the mandatory thai insurance required for oa retirement visas