Smartpak has a cheapie, synthetic fleece half pad that fits the bill if you want very minimal bulk, but just a little cushioning. The price was certainly right, and I'll use it with a thicker pad when not using my Thinline Trifecta.
I've used different versions of Mattes, Fleeceworks, Thinline, Ecogold, Cashel, and Prolite.
IMO the Mattes/Fleeceworks sheepskin is the nicest and provides nice cushioning and wicking properties when used on the horse's back - NOT with a saddle pad. Using a pad kinda defeats some of the purpose of the properties of sheepskin. The Mattes correction pad - ideally without sheepskin to minimize bulk - is also really nice for minor saddle fit issues.
Thinline and Ecogold definitely help in the shock absorbtion category, though I think Ecogold outperforms Thinline. Thing is, the Thinline is thin and some versions are shimmable and the Ecogold triple thick memory foam half pad is not. So saddle fit comes into play.
Personally, for saddle fit issues, the triple pocket Prolite, which is still cheaper than most of the rest at $130, is the best for saddle fit issues. It was developed by a well known saddle fitter and has many, many options for shimming.