I bought a Seat Concepts seat for snowbiking last year for my WR and it made a 150% improvement in my comfort. I also went on a 7-day, 1,550 mile dirt bike ride this summer and never had a sore butt. It's better than my cushy KLR seat.
Guts Racing make some good stuff. Turned my WR450 seat from a 2x4 to a couch. I just ordered my comfort seat for my SXF a few days ago. I'm sure it will be nice too.
I had mine done by Spencer Seat mods. Made a huge difference and it is inexpensive. He is good about getting the mods done and the seat back to you quickly. His website is agreatdaytoride.com or just google Spencer's Seat Mods. He also did my street bike.