Back in my Harley riding days I used an AirHawk seat cushion. IT was made by Roho which makes wheelchair cushions. It is adjustable and once you have the correct amount of air pressure in the pad you actually ride on the air. Very easy to adjust and very comfortable on long rides. Before I got it I tried the air adjustable Harley seat and it simply was not much better for me than the stock seat.
This link takes you to a seat cushion that is constructed and used (different shape) than the one I used.
http://www.allegromedical.com/cushions-covers-backs-c544/roho-ltv-seat-cushion-p550563.html