The one time i had to deal with mites, it was for my dumerils. Luckily they didnt get to any of my other snakes. I just moved my snakes upstairs to a spare bedroom in a glass tank with paper towels and hides and used Provent-A-Mite for 3 months. Got rid of them.
It's true surinames as well as any other boa need a good humidity but i wouldnt call it high. I keep all my snakes between 65-80% depending on the day and season. A couple months of lower humidity isnt going to kill your snake but a million mites feeding on your snake will.
Just relax. While mites suck, they arent the end of the world and pretty much anyone who has kept snakes for years has dealt with it at least once. Usually bringing home an unwanted hitchhiker is the culprit. That is what it was for me.