Hi

Check out the old forum-entries:
the hommade comfort-one: http://www.xt660.com/showthread.php?t=24258
and the ones to buy: http://www.xt660.com/showthread.php?t=22965

The best option in my opinion is a used touratech-seat - unbeatable. One in original size is on ebay.uk.

good rides and cheers

Andy