Morning -
Krylon has a number of products with options of UV protection, a glossy or matte finish, and they even have a "workable fixative" that allows you to protect work that is in progress. You can continue to work on your piece even after protecting a layer. They specifically mention charcoal, chalks and pencil for that one.
They all come in spray cans and I've found them in most craft stores. Can also order online. I've been very happy with their products, and like the range of options. I'm sure there are other fine brands as well - I just happen to know this one, is all.