If it is only your right hip that is becomming sore from the seat, perhaps you are not seated in correctly? Are you sure you are sitting in the middle of the seat? I find that because I am right side dominant, my left side will tend to slouch a lot more if I am not concious of it, tending to force me toward the left side of the seat.

It might sound bogus, but perhaps you have a muscle imballance causing you problems?