I bought one of these:
https://www.amazon.co.uk/gp/product/B01AOUJ2G8
It comes with 2 front screen protectors (nothing for the back unfortunately).
And it does add some excellent grip to the device.
The only downside is that the case is shiny rather than matte, so it can be distracting in the sun.
edit: and I forgot to mention: if you use your gps, *don't* get the aluminium bumpers - apparently they degrade reception and block the gps.