The Era 300s rely on the side walls to reflect sound from its outside side-firing drivers. But the inside- and upward-firing drivers should work just fine with your setup.
Sonos has a 45-day return policy. I would get the Era 300s and test them out for yourself. That is the only way to know for sure if they will work with your room setup.
They’ll sound great. Pull your couch out just a bit, Put one in the corner and on the other side of the couch. I’d recommend the stands for your setup. The ceilings are at a perfect height for both the Arc and ERA 300’s. Ideally, it would be best to put both ERA 300’s near walls, but I think after you finish Trueplay, you will be very happy. As Guitar Superstar said, the best way is to try them. Sonos return policy is no questions asked for 45 days.