Been there and DONE that
Our 02 Bambi has that same coach (btw, it is a Flexsteel). As part of our interior makeover, we recovered it in leather. (we did the work, so this is NOT 2nd hand info).
Part of the problem with the sofa is the material covering it. The fabric A/S used is two layers in most places due to the weave and very stiff. The sofa has arc springs covered with a thick layer of foam. We added another 1" layer of denser foam and then a dacron batting layer over that before putting on the leather. The result is a VERY comfortable sofa and a pretty nice bed. Reupholstering that sofa is NOT for the timid. The pattern pieces are complicated and there is LOTs of them. I also called Airstream and asked what it would cost me to just order a new sofa already in leather (I had seen the exact sofa in the anniversary edition in leather) and they told me $5000 (NO KIDDING!). Obviously, reupholstering it made a lot more sense.
Now everyone comments on how comfortable the sofa is and yes we have slept on it. For some reason, the gaps that used to be so noticable when in "bed" mode, are vastly reduced. Will this design ever be as comfortable as a real mattress, NO, but it is not bad, at least after our improvements. If this was going to be our main bed, I would invest in a layer of memory foam that could be rolled and stowed behind the sofa back as I think that would be all that would be needed. But our use is for naps and occasional visitors, so we just throw a blanket over it and then do the bottom sheet.
check out our pics to see what it looks like now
david & bret
'02 Bambi LS
'99 34' Limited
Air Forums # 2159
Past President Heart of Texas Camping Unit
WBCCI # 7548