Daniel Wolfe I believe you can buy better policies than what you see on the link. The policies on the link just meet the minimum requirements. You can exceed the minimum. Talk to the company of course.
BTW. Follow the logic of your own situation. You have been in Thailand for a year. You can't work as a tourist and you don't have enough money in the bank to last more than a couple of days or a week. That doesn't look suspicious?
Personally, I think there should be an option for people under 50 to stay here longer term. Also . . . there is a 6 month multiple entry tourist visa available. That might have been a better place to start.
Both the Consulates and the border immigration officers have the discretion to deny you entry. They are particularly suspicious if they suspect you are in Thailand working.
As an American you should be familiar with US Immigration having a harsh standard of letting foreigners from many countries entering the US. It is extremely difficult for many Thais to get a visa to enter the US. Consider it reciprocity.