What are your axle and tire ratings? The good news is the list of fifth wheels that would work with that truck is probably pretty short so you won't have too much to sort through. Unfortunately that's also the bad news.
An F150 is a distinct model from an F250/F350. In the latter case the differences range from non-existent to minor and in most cases it's easy to fix any shortcomings. With an F150 you've got a whole different set of components and simply upgrading the suspension really won't do much since you'll still have an F150.