Diztronic on Amazon is always a solid buy. Simple, matte design, feels good in the hands. I've dropped my phone countless number of times, no scratches, dings, dents or cracked screens. For $9.89, you really can't beat that.

I bought my phone two months ago, and ever since I been using Diztronic Ultra Case . I have had 5 or 6 drops varied from 1-4 foot and it has survived all. there is also a drop test video for this case, you can find it on Youtube. Take a look at this topic too. about your second question, I'm not sure about the warranty but any modifications to system will prevent the OTA from being installed .If you dont want to install updates manually, you can flash system ( which literally unroots and clears any modifications to system ) and attempt to install OTA and then root again, etc. iirc you can sideload updates too but I haven't done it so I can't say.

Diztronic on our phones here. Cheap, hold up well, not slippery, don't get gross overtime. Not the thinnest but a good trade off. Wife has dropped her old Moto X and her now 5x multiple times and never broken a phone. Good enough for me.

https://www.amazon.com/Nexus-Diztronic-Matte-Flexible-Motorola/dp/B00PYKPX8U

So I have this pad which works OK on this case but the positioning is a bit too 'exact' for me. I also got this dock which is much better. I've just ordered this one too for a different desk, which hopefully is going to be the best of the bunch.

They all work though, the dock is pretty cool just to be able to grab and go from the night stand.