I park mine in a Krungsri Mai Te Dai account... OK, only 0.9% interest, which is taxed, but it comes with a bank book, and because every month there is an automated Interest entry, Chiang Mai Immigration don't need a statement, just the book, & a letter confirming current balance when I apply for the extension.
You can withdraw at any time, so if the proverbial hit the fan for any reason (medical etc), you can use it and replenish later, which I guess is not true of a Fixed Bond.