I got a matte black diztronic tpu case, it fits very well and has all the correct cutouts. I really like it and it doesn't add much bulk. Check it out.. Nexus 6P Case, Diztronic Full Matte Slim-Fit Flexible TPU Case for Huawei Nexus 6P (2015) - Black - (N6P-FM-BLK) https://www.amazon.com/dp/B017DU6GMK/ref=cm_sw_r_other_awd_yUcPwbHWD6DJ8

I've had this one on for a few months after having the same Spigen problem. The clear back has developed a few small scratches that you'll notice if you look close, though. If that bothers you, I think they have a version that's solid throughout. Buttons aren't cut out but never give me a problem. Great option for the price. Hopefully you can still find it elsewhere.

Edit: The solid option