I waited 4 years to replace my OEM seat with a suspension. 4 years too long.
I used two 2x6's to fabricate the new bolt pattern line up for the seat, and still use the existing hole pattern on the tractor deck. By doing this it also raised the seat 1½" which was just fine with my long legs.
The big measurement you need to watch is the width of the seat, to make sure it fits between your operating levers on each side of the current seat. Moving and refabricating levers is no fun.
But like Rgr33 said, it smooths out the ride, but not like a car suspension.