Asking for trouble if you ask me.Apply for non immigrant O in your own country.That gives you 3 months.You can open bank account on your own no problem which is what I did.After 2 months convert non O to retirement visa.Using an agent causes lots of problems when you go to renew retirement visa again.Im assuming you have the 800k to deposit.
You can't with a tourist visa.Ive tried several times.The best way is to apply for a non immigrant O in your country.Gives you 3 months then convert to retirement visa.Opened account first day no problem.
Apply for a Non-immigrant O visa in your country.This gives you 90 days .Then convert to retirement visa in Thailand .You have to immediately open a bank account and deposit baht800k each.This amount must remain in account for 2months before applying for retirement visa.Cost is 1900 baht.