From what I've hear over the years, there is no better, more comfortable seat than the Russell Day Long. Going there to get it custom fitted is the best of all worlds. You can decide about heating when you get there. I would get the best looking, most durable covering available. That's probably vinyl. You can check out what it looks like and also the different patterns. Are the stock shocks not working for you with 2 up? If yes, don't waste your money on different ones.
PS: Forgot to suggest getting a backrest. Russell uses the stock seat pan to build a new seat.