I’ve been looking into solutions for this as well and want to try an ultrasonic mister disc. They’re cheap and seem like they would be pretty effective.

Something like this is what I’ve had in mind. Even the small ones produce a pretty large amount of fog so it would probably be best to run it off a Humidistat.

Edit: looks like I also didn’t know fog isn’t a good way to add humidity for tortoises. Cheers, good luck!