I had the Black/gold neo hybrid case on my Nexus 5 and I loved it. Great looking case, but it added a decent amount of thickness and heft. I imagine its going to do the same on the GS6. Just be aware of that.
The only other thing you need after your new case is this and the company even made me a custom one for the back when the one supplied was a little off in size
Another vote for Ringke. Perfect fit, perfect grippiness and as slim as any case can be while still protecting the screen and camera. An absolute steal at $9.99. I love mine.
I have been using the neo hybrid case for a few weeks on my S6 and really like the case. It has a classy look and does not add a large amount of bulk to the phone and charges wireless no problems. I have a Zagg tempered glass protector with case and makes a perfect combo in my eyes.
No I do not feel it make the phone slippy.