I spent two nights on one as a guest. and I must say-it was the best sleeper sofa of this kind (hidden mattress folds out) in my life..well among ones I tried So yes I'd say it's worth it

Did you try Apt2B?

Return it for a real couch and buy a blow up Aero bed for sleep overs. : ) There really isn't a sleep sofa that feels like a regular sofa. You use these in rooms where the couch need not BE as comfy as your typical family room sofa. A study, perhaps. Otherwise? Lay some foam on there and buy a ready made stretch to fit slipcover for the entire piece. Not great as both will have to come off for sleeping. Your idea? No.....will turn to ugly: ) Keep a stack of 24 inch square toss pillows with down fill, and plop em on when you sit. Contrasting color? Who cares. Don't keep them on the sofa full time.

Don't recover it unless you find it super comfy AS IS. By the time you do? You could start over with a new sofa. Trying to build a support within is a no go. You'd be far better finding a consigned quality sofa.....and recovering something previously enjoyed. Local to you, if at all possible.