The stock seat isn't really that bad, comparatively speaking. Just ugly. But a big guy should fill the whole curve of the seat and get good support.
Another thing to look into for long runs might be an Airhawk. They do genuinely work on eliminating hotspots.
I just put a Mustang seat on mine. Awesome in most ways, but holy hell was it snug. And by snug I mean I had to put a strap around the front brake to create a parking brake, lean with my full strength/weight against the rear of the seat with the left hand and shove it forward against the tank with one hand until the seat cover wrinkled up against the tank, insert bolt... and then the real hard work began of trying to get the other mounting tab over the mounting hole by literally hanging off the lower lefthand part of the seat to yank it down and forward. It's pretty much a two-man job, only barely managed it.
But it sure is pretty, and fairly comfy already, does need some break-in.