Financials for my latest extension at Jomtien (late October):
12 month statement,
Copy of each page of bank book (going back 12 months),
Bank letter stating that I hold an account (BBL) and current balance,
Separate bank letter listing each of the monthly foreign transfers,
Proof of where the money came from. I produced a letter from my pension provider, showing the monthly and annual amount - this was accepted.