It is good that your snake is otherwise looking healthy. Add a touch of dish soap to your bath; it helps break surface tension to better drown the hiding mites. This will largely reduce numbers, but will take a bit of luck to get them all. For best, quickest results, use a chemical anti-parasite. I wouldn't choose the flea collar method is it has more potential to overdose your snake. Provent-a-mite seems to be the most readily available product; you could probably buy it from the same petstore that will sell you the flea collar. Follow the instructions on the bottle.

Remember that mites travel, and you need to treat both the snake, and the environment to get rid of an infestation.

Ian