As long as we're talking the couch bed, and air mattress on top should be no problem at all. Personally that's what I would do too. The weight limitation would be of the wood framing, which is pretty sturdy. I don't know what a weight limit would be on it, that info wouldn't have been in the owner's manual anyway, but I would guess upwards of 400 lbs. Luckily you don't have far to fall should it collapse, but unless there's water damage with it, I doubt that would happen.
The cabinet bunk(s), if you have them, where the cabinet looking thing folds down to create an upper bunk, are only rated at 100 lbs.
Another option to improve your couch, both for sitting and for sleeping, is to get new foam for it. Since you're from PA, we've had some members have good luck working with Page Foam in Johnstown. They were the original supplier of Sunline cushions in the '90s and '00s. I'm sure they could sew you new covers if you absolutely needed, but I think if you just gave them dimensions, they could sell you just new dense foam to put in the cushions. This would give you a much better surface that you wouldn't sink so far into. Here's Page Foam's consumer division: CamperMattress a Page Bedding Company
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR