I'm also not a fan of cases, but I had to do something to combat the slickness of the S6, both in hand and also lying flat on a smooth surface. I ended up getting the Samsung clear protective cover and it's everything I want from a case:
1) It only attaches at the corners, so all of the sides and buttons are open.
2) Since the sides are open, it adds no extra width and only tiny amount of thickness (it's flush with the camera hump).
3) The handling of the phone improved exponentially. I can now comfortably and confidently reach all corners of the screen with my thumb. Grip is now outstanding.
4) The corner of the case juts out a bit, just enough to prevent the base of my thumb from touching the edge of the screen. This was annoying when reaching the far sides of the screen because the edge touch inhibited my thumb touch. In some apps, it actually activated stuff I didn't want.
Basically, this is the case for people who don't like cases.
http://www.amazon.com/Samsung-Prote...ag=hawk-future-20&ascsubtag=UUacUvbUpU4403858