I'm a little over 6' and have recurring back problems. I haven't changed the America stock seat (which I find very comfortable) but I always use my Tombstone Backrest Bag on trips (it only works with a sissy bar). All back problems are different and you need to figure out if it's not being able to relax, reaching for bars, or seat position. All those things are fixable.
I'm sorry to hear bad comments about NewSpeedmaster.com. I've bought a lot of stuff from Brent with absolutely no problems. The company is mainly a reseller and doesn't make the chrome they sell. All the chrome pieces I've bought have been fine (license plate frame, handlebar end caps, sidestand pad, etc.
