Just have a copy of an outbound flight ready in your hand within the 30 days visa period expidia let you purchase and cancel without any costs involved
Show this to any over zealous immigration officer and maybe have a recent ATM slip handy proving you have funds and you will definitely be okay
I recently got pulled over entering Suvarnabhumi airport after my T/R visa and 30 day extension ran out
Like your thinking now I went to Danang for a few days and re- entered on a visa exemption but the immigration officer called over the supervisor and after a few minutes pleading he said okay this time 30 days no more tourist visa for 6 months and advised me to get a Non O visa next time
You also get from the bank at the same visit a ATM card and a Bangkok Bank account book
They (Tik Tok agency) even paid 500 baht into my account when it was opened so I give it back to the girls in the office as a tip for the excellent service from the staff 👍