I'm going to Tibet to take photos in September. My camera is a Sony nex-5r dual lens. Do I need to buy uv mirrors and polarizers?

In order to protect the lenses, you should wear ultraviolet glasses.

As for CPL, do you want it? Tibet is sunny. If there is a large area of water in your photo, you can use it to eliminate the reflected light. You don't have to use it in other cases. As for making the sky bluer, it is actually a little bluer. Of course, it doesn't hurt to match it, because it will always be used. Although the chances of using it are not great, I still suggest wearing a gradient lens.