Research ABG substrate. It’s the gold standard for dart frog keepers. You can find a recipe on most dart frog forums or by searching google. You can find one and tweet it as you need. The key is tree fern fiber. I’m not sure you really need it. ABG is really designed for high humidity cages where you need something that will not rot or get too water logged. A good quality organic soil will probably be fine. Just make sure it is truly free from any chemicals. The problem I see is that heat sources will usually kill your plants. You can make a bio active with just isopods and springtails. Throw in some leaf litter and a lot of pieces of bark and your good.