Here's a very slim leather case with microfiber on the inside. All the buttons are accessible and on top of that: room for a creditcard!
http://www.mujjo.com/the-sleeves-collection/leather-wallet-case-for-iphone-6-black
Looks very nice. But I don't like the idea of room for a credit card. Maybe it's just me, but it seems off-putting for some reason, like added material that offers no real benefit.
I'm also wondering if I actually want a case with accessible buttons. Is it my imagination, or are the buttons on the naked iphone 6 hard to locate and push, and some cases actually make it easier to use?