Our 2013 8289ws came with the air mattress sofa. The pathetic original air mattress only lasted a couple of trips but that turned out to be a blessing in disguise. I replaced it with a decent air mattress (purchased from Amazon) and am satisfied. I have found that even with a better air mattress, I prefer to just place it on the floor rather than the sofa foldout (far more stable and less chance of puncture).
So based on my experience, I suggest you keep your sofa and just buy a decent air mattress to use on the floor.
'04 GMC Sierra 2500HD, CCSB, D/A, MaxBrake, B&W Companion, Retrax Pro, AR Power Steps
2013 Rockwood 8289WS w/Diamond pkg
1969 Camaro RS/SS Convertible
Dad's old 1968 Empi Imp (recently recovered from under 21 years worth of boxes/dust)