You can undeniably improve the quality of your ride by changing suspension, but that is not going to make you more comfortable! I also caution against using any add on pad, as that is still not addressing the source of your problem, namely what sounds like a crap seat!
I have a Sundowner on my Dyna, which is made in both solo and dual versions, not sure if there is a Sportster solo version. I have a Corbin 'bucket' seat on my dresser, which gives a wide shaped firm cushion, which is remarkably comfortable, although my wife finds her department less so.
Seats are a difficult topic, simply because there are a confusing variety, most of which you can dismiss as far too many concentrate on looks rather than comfort. So Harley touring seats, Mustang, possibly Corbin.
If you want to look cool on short trips and be comfortable on longer ones, then you may need two seats.
