I don't like using sand of any sort for non-desert dwelling snakes due to it's invasive qualities (sounds like it's really bothering your snakes too).
I used astro turf/carpet type substrate for a number of years but it was a pain. Hard to tell if it's really clean since moisture just seeps through and settles at bottom. It took a while to dry out too, so I had to have spare pieces to swap out during cage cleaning.
Some people have had good results with aspen shavings, but you should watch when feeding the snakes in the cage because they sometimes swallow it with their dinner, which can lead to impaction. Also, even with spot cleaning visible waste every few days, it can still get pretty funky. When I cleaned out the whole tank, I usually ended up with half of it on the floor which doubled my clean up (ok, so I'm sort of clumsy too).
I prefer paper substrates like paper towel, news print, or heavy craft paper. I know when they're clean, they're absorbant and not likely to be ingested. It also makes cage cleaning really simple which is always a plus. And if you ever end up with mites (hope you don't, but it seems inevitable if you keeep enough snakes long enough) paper substrate is the easiest way to identify them early and start your treatment regimen.
Just some observations based on my snake keeping experiences.
Lora