I just bought one to renovate my 10 year old fifth wheel. The manufacturer on mine says Villa International Rv furniture.
http://www.villainternational.com/
They aren't cheap so get ready for some sticker shock when you look into it. I looked for a while and then got lucky and found what I wanted on Craigslist for a small fraction of the cost of a new one. Mine is the L-shaped extenda lounge. The L part has an extendable seat section. There are options you can add to these types of sofas. Mine has a queen bed in the straight section with flip up foot rests as well. All comes apart to fit through a 24' door.
You say you want very comfortable. You would have to decide if this type would suit your needs. Everyone that sits on mine loves it though.
Another option, of course, is to take out a window (usually the dinette window) and bring the new couch in that way if the window is big enough. While it's not ideal for everyone to remove a window, this method now allows you to buy whatever couch you like providing the window opening is big enough.
2008 Chevy 2500hd Duramax/Allison
2006 Wildcat 27 bhwb
2009 Lance 830 *Sold*
2011 Northern Lite 8.5 *Sold*