I like keeping my stock seat. Because it usually cheaper for the super sport tail mainly.
But if you go with the sbk tail then I would suggest a seat from woodcraft like suggested above. I use a lot of their stuff and I have found all of their products to be top notch.
Theres a guy on the SVRider forum that makes tank pads called HammerGrips. They are an 1/8 inch thick foam pad He can custom cut them to any size or shape you want. I bet he could do one that would make a decnt light weight seat. I havent seen him do it but just a thought.