I replaced my OEM(Lippert?) sofa with a Belmont from Shop4Seats.com. Both sofas went through the door very easily after I took them apart. The Belmont is a huge improvement and is very comfortable to sleep on. Compared with the one in the picture above one feature I like about the Belmont is that the arm rests are removable so that you can the use space the arm rests take up and can even hang feet of the end if needed. It has an optional storage drawer underneath that is easy to use.
http://shop4seats.com/rv-furniture/sofa-beds/jack-knife-sofa-beds/belmont-sofa-bed.html