Seats:

Fury seats only fit the Fury.
All other VT models can swap. There is only one or two companies that make a solo seat however for the non Furys.

My butt hurts, which seat should i get?
Well, sadly only your butt can answer that question. Many people can offer an opinion based on their asses response, but it may not even be better than the stock seat to you. The best bet and cheapest by far, is to get the Air Hawk cushion. Its adjustable and is about 1/5th the cost of a Mustang or Corbin.

I would add that a good upholsterer can pad up the Fury seat as much as you want for a fraction of a replacement seat.