Seat Concepts is now offering a complete bolt-on seat for the 2008+ Yamaha WR250X (and WR250R) which consists of their seat foam and seat cover installed on a Spiral seat pan. The seat bolts right onto your bike in a matter of seconds using the OEM mounting points (2 bolts).
I've been riding with Seat Concepts seats on my WR250X for the last few summers. I run the low foam version, so not only does it help me with the bikes tall seat height, but the seat is also much more comfortable than the stock seat thanks to a wider seating surface and slightly softer foam. I've done several 250+ mile days with no issues... couldn't say the same thing for the stock WR250X seat!
NOTE: Seat Concepts still offers their "seat kits" if you want to save some money and use your stock seat pan to install their foam and seat cover (see "Seat Kit" link below).