Go and get it done early, as Robert Lagos says, your extension is added to your current stay. You lose nothing, but will have peace of mind knowing everything is sorted.
Steven de Blaquiere I don’t find transfers too much of a problem, I use TransferWise whose fees are quite reasonable. I do however find it very strange that they expect us to deposit approximated three times the average Thai wage every month.
I agree, I normally spend a couple of months back in the UK during the summer visiting friends and family. I will still have to transfer 65k THB into my account here. However, I suppose at the end of the day, rules are rules and we have to comply.