We have done some work on our 5th wheel over the years to make it more comfortable. Luckily our sofa sleeper is comfortable both as a sofa and bed.
We did replace the recliners with two from Lazy Boy...much more comfortable.
We replaced the bedroom mattress with a sleep number mattress.
Ours didn't come with an electric fireplace, so I installed one both for the ambiance and for the heater feature. Since we installed the fireplace we haven't used the forced air heater the fireplace heat keeps us comfortable.
Keep in mind because the doors are narrow, some furniture is installed before windows go in at the factory, so be sure any furniture to removed or installed will fit through the entrance door.
Make it comfortable and you'll enjoy it more.