Glad to have you here with us in the forum.
Just about any furniture that will fit through your door is okay in an RV. However if you want a sleeper sofa with seat belts, not many residential sofas will fit the bill. There is no single place where you can get the best deals on items. Determine what you need, and do a Google search to find it.
Tony & Ruth........... FMCA#F416727
Newmar Dutch Star 4320, Spartan MM Chassis, Cat C9, Jeep Grand Cherokee,with Hemi, hooked up with a Blue Ox Aventa LX, and Brake Buddy.