A buddy of mine modified the stock seat on his SV650S and the results are pretty amazing. He added some material for height, used a better cover and reshaped the seat to remove pressure points, offer support where needed and and soften it where it's not. The modification took 2 tries to get what he wanted but it was as simple as removing some staples, cut here, grind there, add there, stick it down, restaple done.
Here's a link: http://www.diymotorcycleseat.com/index.php
Anyone able to comment on their modification?