Thanks, Gail! I'm eyeing a J-style sofa with slideout now, because most times when I lie on the sofa at home, it's lengthwise on one side of the room facing the sofa, so I'd probably get the most use out of that:http://www.glastop.com/rv-furniture-detail.asp?id=663
I like that, especially if you delete the lower arm so you can use the whole length as the sofa. I only use about 48" of my sofa when I'm lounging (I measured) so 54" would be decent. (And I wonder how hard it would be to include some velcro tabs and a little ottoman to make a little extra length in the jackknife.
A quick drawing (not to scale or proportion!) to illustrate. Blue is the J-lounge (no-bump model) in the slide, red is the jackknife, yellow is the ottoman, and they would all be flush together.