Many here on the forum gonna suggest you leave the bottom bare for a good reason. Its easy to clean and with that amount of misting you do in that glass terrarium it would easy grow mold or overflood. With more work you could maintain a good substraited enclosure but its more complicated. I would recommend you to google articles on bioactive terrariums for advise IF you're prepared to do it.
The bottom gonna have to look something like this:
1. A drainage possibility. (Works as easy with a small cut in half plastic bottle at the corner. When its time to drain you just drain it like an aquarium with a hose. You don't want too much water pool up at the bottom as it may collect bacteria. Get rid of it as soon as possible.)
2. A thick layer hydrograins or rocks. I use hydrograins as they absorb water.
3. On top of that place a barrier membrane of cloth (not regular fabric) or mesh to separate this layer from the next
4. Plantarium soil. Easy to get at a petstore. Absorbs water MUCH better than regular soil that would easy grow mold
5. A cover layer. For this I would go for moss, big thick moss that stick together and wont fall apart if your cham would miss an insect and get the moss instead. I do not recommend to use bare soil of any kind if your chameleon would by chance eat some
It's a bit harder and you can't skip one of these steps and expect your enclosure to do just fine. Its therefore easier to go just without it
Good luck!