No. Prepaid is fine. Your phone number is registered with your passport and the bank can match that if they so desire.
If your bank is going to send OTP's then just turn on the Thai SIM in your phone. My bank doesn't, and authorisation requests come through the app itself, no phone connection needed.
So the steps are simple, get a phone, get the app, try to set it up yourself (you will need to be in Thailand when you do it) and if you can't pop into the bank and they will do it for you.