You state that your monthly spending is approx. 25,000 Baht.
Now, if you have bought your house, then I know that is possible, but I find it hard to imagine that this 25K also includes health insurance for a 76 year old. I advise you to check your coverage as it may not include full coverage.
Your pension is 35K so you have scope to increase your spending each month and still not have to touch the money in the bank.