The Renaissance also has that option for a "family suite" with their so called 1 bedroom suite and adjoining studio suite.

Also you may consider the Surawongse which has 1 and 2 bedroom suites. While the Surawongse is also usually generous with giving these off to elites, I agree with that old adage to just book the room you need instead of waiting for an upgrade (and to be disappointed at check in). Bangkok is busy all year around and Bonvoy properties are always popular.