The iPhone 6 is a beautiful piece of hardware, but as the iPhone itself continues to slim down (and become rounder on the edges) it does become a little harder to grasp. When I first got my iPhone 6, I was on board with others that felt it was just a little too slippery.
TOTALEE's The Scarf, also available for the iPhone 6 plus, touts itself as the thinnest case in the world and it holds true to that claim. At .35mm thin with full cutouts at the bottom, the case simply stays out of the way while giving you something to hold onto. As stated, it's not going to support your phone on a long drop, but it'll stop scuffs on the back and do its job well in typical use.
If you are a no case type of user but found yourself needing one with your latest upgrade, give The Scarf a try.