I travel to bkk relatively often and have some tips for you. Going thru tpe is a good option, Eva air down to bkk. Short flight and easy airport to connect thru.

If you go thru pvg or pek and don’t have a visa, simply buy a refundable ticket on another airline showing you leaving China that day or the next. Just buy it on a airline leaving from the same terminal as the you want to Nonrev from. Lookup transit without visa for more details. I think you can have up to 3 days with having to get a visa. Once you clear inbound immigration you can cxl the ticket and nonrev as you wish.

You might look as just buying a confirmed ticket from one of those cities to bkk, often pretty cheap.

Bkk has a metro to the airport now that is pretty convenient...takes the hassle of the traffic out the equation.