I wish you the best. I did purchase new seats for our Class A that were more comfortable and offered more support but after the operation I discovered that I really didn't need to go that far.
Since you are looking at a used unit, find the floor plan that works and ask for past service records. The coach will be out of warranty and all of the systems are repairable. Find a unit that was used regularly, and maintained, and has a floor plan that works and you can't hardly go wrong. Opinions will go all over the place about which brand is better but I feel the floor plan is the most important and during an inspection you will discover poor quality if it is there.