My cousin and hubby were going to change their sofa for 2 recliners. They found 2 problems - one, getting them through the door. The old sofa, they could have dismantled, but the only chairs they could find with a lift off back were Lazy Boys and were pretty $$$ x 2. The second was that to do what they had in mind would have left holes in the flooring, so that would have required replacing to look nice. They decided to just live with it for a while longer, have sold it and will look into a new trailer in the spring.
Our new TT has a really quite comfortable sofa with a fold out bed with air mattress. I hadn't been a fan of air mattresses, but this one is very comfortable and has a built in pump - inflate in about 2 minutes or so and about the same to deflate. Don't know the measurements, but it's a FR Rockwood Ultra Lite and they could probably give you the supplier. It sits snugly between the dinette and outside wall in the slide. Have no idea if it's actually attached to the floor because we've never tried to pull it out, but it does have sorta donut shaped "feet".
Valid point about it possibly being a pass through - maybe an issue for you, maybe not.