Tom,
I have a jack-knife sofa similar to yours in my 2003 Alumascape TT. I also would like to replace it with a more comfortable sofa or 2 recliners. The problem in my rig is that the sofa sits in the slide-out but the slide-out does not come all the way down to the floor. It stops about 12" from the floor. I believe this may be your problem also. Basically what I need is a couch with no legs or 2 recliners with 12" legs that I could remove. So far I have not been able to find this. In the meantime my wife has managed to install extra foam in the sofa. It is slightly more confortable but 2 recliners would be my dream. Dale