many over 70 (typical expat on a non-o) will find health insurance very expensive with many exclusions. If over 70, expect to pay about ฿15k/month and may find that many issues will be excluded as preexisting conditions. Insurance here is archaic.
The point of the 800k is that it is to be accessible and liquid for medical (and other) emergencies. I don't believe a fixed account would qualify since the funds aren't available to you.
I'd talk to a lawyer since a non-o does not give you the right to work .. as you've already been advised, it would be best to twin and open a bank account in your home country and remit funds to Thailand as needed.