If you have 800 K in the bank , that is a no-brainer unless of course you don't want to tie up your money in the bank . Simplify your life & get a retirement visa & show 800 K in the bank .
I opened a bank Accnt thru Bangkok Bank in Chang Mai . At the time I was staying in a condo for 3 months . The manager registered my stay @ the Immigration & I had a copy of the contract . I took that to the Immigration , got my letter of residence . I paid 500 baht and the next day I took that form to the bank .
I used a thai visa agent in Bangkok . Its a reputable company , theyre on FB , theyre on Line . They're responsive , speak English & great customer service . I'll send you their contact # if you want .
Save yourself the hassle & use an agent to do the retirèrent visa & if you need assistance in converting a tourist visa into a non 0 visa they'll help with that you . That is one option