Why have you maintained the 800k for all these years? Don't you regularly bring money into Thailand to live off because you could have switched to the 65k monthly transfer method a long time ago?
You can't get a Non-OA from inside Thailand as it has to be in your country of residence but you can also get the Non-O based on income if applying from there
How long are you intending to stay and, more importantly, are you planning on getting the 12 month extension? Also consider if you start again on a Non-O your annual extension will be on the date when that Non-O expires every subsequent year, will that be an issue for you?