There are several different visa that retirees can use to live in Thailand. They have different financial requirements and different structures and benefits. The O visa, described by Brandon, is the most popular retirement visa and has not changed in many years. Some of the other visas are targeted towards wealthier expats.
You should look at the Elite Visa program and the visas offered through the Thailand Board of Investment (BOI). Either way you will be paying a fairly large sum of money for a long term visa (not permanent)
I’m guessing they will want you to pay with real money.
For the monthly method my understanding is that your 1 year Thai bank statement must show that you have deposited at least 65,000฿ each of the previous 12 months into your Thai bank. The deposits have to show that they originated outside Thailand.
I believe you have to use the 800,000฿ deposit method for the first year extension and then you can use that year to establish a record of monthly deposits
Also, by verification letter, I mean what is often called the bank letter which just states that you have a valid account, the account number, and the account balance at the time of the letter. It doesn’t address something like monthly income.
Several major embassies, including the US, stopped issuing income verification affidavits in 2019. Since then you get a account verification letter from the bank and a 1 year bank statement plus your bank book with a same day transaction. You don’t need anything from the US embassy to get a 1 year extension at Bangkok Immigration