I had a spare thou seat converted into a single seat + hump by a chap in Penzance.£80 this mod is great in that I can rest my arse against something when I wind it up. The chap in question measured me and my position on the bike. In the case of this mod it was essential to get the hump position just right so I am glad that I went to a local (to me ) company. Depends on what type of seat you want as there are lots of different types, but if you are a short arse extra material could be an issue