I believe that mattresses are somehow exempt in the US? So the futon becomes a weird gray area. You can buy one with the express intent of using it only as a couch, but you put a mattress on it. I'm not 100% sure to be honest.
Do your own research, but from what I found it’s not too hard to be careful about this stuff.
https://www.ikea.com/us/en/files/pdf/5c/df/5cdf003d/ikea_faq...
The underlying problem here is that furniture doesn't need flame retardants, period. You wind up with this weird mouse & cat game. A drive to replace one additive just find something new, previously unknown, and possibly worse.
For example banning lead additives from gasoline was a good thing. It was replaced with MTBE which causes to groundwater contamination. This has now been banned in the US, which ironically sees ethanol replacing it. Ethanol production obviously predates gasoline, so it could have been used all along.