i have a 2009 street glide seat is uncomfortable, no back support, looking at a 2012 road king seat or 2012 street glide seat is there much differrence

 

SG seat is contoured for looks to remain more low profile to the bike, not for comfort. The RK seat might help, but it's not going to offer back support. If that's what you're after, you may want to look at a backrest before seat swapping. Go to a dealer to sit on other touring bikes to see if you find a seat more comfortable.

As always, there are tons of aftermarket options or you can try to have your current seat modified to meet your needs.