Surely you know that you can't simply change the diameter of the tire without changing wheels as well, and that is going to be a really expensive change with very little payback.
As for the larger tires riding better, that is debatable. It may be true on a chassis designed for the larger and heavier wheel and tire, but adding them to your light and short chassis could just turn it from a "Bread Truck" ride to that of a "Log Wagon".
I have an older 16" wheel coach and I hear folks with the 19.5s and the 22.5s with the same complaints that I have.
Weigh your coach and set the right tire pressures.