or apply for retirement visa, no health check, no criminal record check, just show funds available, health or travel insurance for said amount,
arrive with your 90 day visa, register address with immigration, get letter from them to say you have an address, take it to the bank, open 2 accounts 1 for the 800k transfered from your home country, the other account for general living.
Once the funds have been in Thai bank for 2 months, go back to immigration to get your 1 year visa, you renew every year, but you don't have to show insurance for renewals.