just to give you some further info because this is what I did. You don't even have to use a lawyer to make a legitimate will in Thailand but I did just for convenience. It cost me 10,000 baht. It took just a couple of days to finalize the wording which was in both English and Thai and then signed by myself, the lawyer and two witnesses. In the will the accounts I wanted to bequeath were written into the will. I gave one copy to my wife and the other copy was retained by the lawyer for safekeeping. Any local lawyer's office will offer this service.
Of course you will get contradictory answers if you come on to a group and ask what you are able to get away with if you don't follow the law. Everyone will have an opinion on that.
it's very straightforward if you are used to making payments by scanning a QR code with your banking app. You set up how much you want to withdraw beforehand and when you select cardless withdrawal on the ATM you're presented with a QR code which you scan with your phone and out pops the cash!