Is it possible to do bioactive without isopods?

[Oxylepy]

Personally I dig up soil from outside. So I have worms, roly polies, centipedes, springtails, and millipedes in there as my clean up crew.

You could attempt something similar without the spring tails by:

Buying worms from a bait shop
Collecting outside wood for roly polies, isolating them and being certain there are no other insects with them.
Digging/outside wood for millipedes

Centipedes are kind of up to you. They are predators that eat insects, they tend to keep the other populations in check. HOWEVER your snake isn't going to eat the centipedes, meaning they could get out of hand. It's up to you, but if you add them exercise caution that they don't end up throwing the whole thing out of balance or trying to eat your snake.

Freeze leaf litter that you bring in. The insects will eat it, it will help maintain soil humidity, but it also will carry everything into your house, and since you want to avoid certain things you have to kill them before they get in.

Edit: The more elements you add to your ecosystem the better off you are. DO NOT ALLOW CRICKETS IN, they are impossible to get rid of without scrapping the whole thing and they need additional food added in that will rot. They will keep reproducing and may attack the snake.

Another thing you can consider is adding other reptiles. By that I mean geckos. At which point crickets and centipedes won't be an issue at all, and crickets may become useful to the ecosystem. This assumes your snake won't eat them, as my savannah monitor did when I added the geckos to fight the crickets. You also need to be careful about the gender of geckos, specifically you will want all females, otherwise they will breed, and you will have a bad time.