The first thing you'll probably notice is that a residential sofa is bigger than the one you're replacing. And it may weigh more, so you might be adding quite a bit of extra weight to your coach. Check the dimensions of where you will be placing it and then carry a tape measure with you to the furniture store. And yes, you will definitely want to secure whatever you get to the floor. The seat-belts aren't going to do much good if the sofa goes flying through the air. ;-)
We just removed the sofa and seat-belts from ours and went back with a futon-style sofa from World Market.
World Market Studio Day Sofa I used some "L" brackets to screw it down to the floor and it works like a charm so far. Of course, we also removed the dinette set/benches and put the studio sofa in it's place. The original RV sofa was in the slide and we are on the hunt for a decent table/work surface for that space. We don't have anyone riding with us, so we had no need of the extra riding positions, and we never used the dinette for anything except to catch "stuff", so we changed it around. We also removed the recliner since we never used it either. I turn the driver's and passenger's seat around and use ottomans as foot props.
In doing all that we shed quite a bit of weight and made the RV more usable for our purposes.
