Our first hard sided travel trailer was a Dutchmen Sport Lite. It had a jack knife sofa / bed in the living room area. And yes, it was horrible. I don't think there are ANY jack knife sofas that are actually comfortable as a bed. Folks have tried to put memory foam on top of them. Other than that, there's not much else you can do except replace the sofa..... which will probably be as uncomfortable as your original.
How did we "solve" our's? Well, after 18 months of fighting with a corner bed and crawling over each other to get up in the middle of the night or to go to bed, or for any reason, AND that jack knife sofa that was horrible uncomfortable, as a couch AND even worse as a bed, we solved the problem by simply getting another trailer that had a walk around bed and a normal (non jack knife) couch. That one lasted for 8 more years. That was our solution.
2019 Montana High Country 375FL
2014 Chevy Duramax HD 6.6 - 3500 Diesel Dully Long bed Crew Cab