I am 42, married to a Thai. I have a degree and TEFL cert. I have been teaching for 15 years but unfortunately bad health means that I can't work much any more.

I would though love to work about 12 hours a week, but no more than 4 hours in one day. Is there any way that this is possible?

In no way would I like to do something illegal and risk my visa.

It is possible, the greatest difficulty would be to find a school that will employ you for only 12 hours a week. But it is possible to get a work permit for part time work.

You might also try to find work teaching English to hotel staff etc....probably easier to find for just a few hours per week.