Eco-earth or coconut fiber will work.
Don't soak it. Think fresh potting soil.
Still small enough that you'll want to keep the humidity up some.
I like to give them a dry spot so they have a choice.
I bake everything around 200* for an hour or two. Depending on the batch.
Just keep an eye on it so it doesn't start to char.
You could still get wood mites. But they won't harm anything. Google "springtails" if they pop up, count it as a freebie. Some people have to pay for them. I have found them in with a few of my Ts, make great clean up crews.