How many cases have you gone through until you found the right one?
My first one was a Encased Rugged. It was sturdy but too slippery. It was hard plastic all around including the sides. There is some texturing on the sides but still very slippery.
I'm currently using a Ykooe which had TPU material on the perimeter so in terms of grip, it is better than the Encased. However, the back is similar to the Encased Rugged in that it is slippery which is not a problem when I'm holding the phone, but when I lay it flat, it slides too easily on the car seat for example. Can someone recommend another case? Or there is something I can affix to back of the case that provides a non-slip surface?