I started out using aspen for my kingsnake and now I use a mixture of cypress mulch and coco fiber. I know you mentioned that you don't want to use coco fiber but I think I can still recommend switching off of aspen just for the fact that coco products don't mold and you don't need to worry about spilling water or not being able to raise humidity. I haven't had any dust issues so far.
I've also been looking into hemp because it's more sustainable than cypress and seems just as effective, so I'd also love to hear if anyone has experience with it.