It is really hard without all the paperwork or an agent … i had just about every document under the sun including one year visa extension yet was refused by two bank branches this week for most minor things on the long term lease and surname before first name on the residence letter from immigration ; 3rd time lucky today when kept trying (and because it was nearing the closing time rushing through paperwork). On a tourist visa not possible on your own. You will need an agent.
rule …. No such thing in Thailand. Extend and Border run as long as you can get away with it is the rule in Thailand: you will know as you will be warned ( “this is last time” the immigration officer will tell you, usually they do not refuse entry….). They however can start looking at other criteria which could be used against you: exit route out of the country within 90 days, 20,000 baht on you, booked accommodation so being compliant after few extension and border runs is crucial.
the letter i am picking up on Monday addressed to only one bank i had to nominate. The letter however free (but it takes 5 working days). Different IO do things differently.