The question is hard to answer because of the unknowns and variables. It all depends on things like; Amount of use, Type of use, density of foam, liner, cover material and weight of the user. Basically, Twiggy’s cushions are most likely going to last longer than André the Giants.
If you are hitting bottom, you might want a higher density foam. If it feels like a rock, lower density is indicated.
Welcome to Lake Wobegon where Justin and David utilize abductive reasoning to help solve F/SS issues.
Happy Trails and Remember the Pequod.