I've got floor tile (linoleum) in the bottom of one cage - works great. Its not stuck down with anything yet, but I plan to seal it down with aquarium safe silicon. The other cages are painted wood bottoms, some with paper towel or bath towels on top (to catch errant drips).
There's no law against substrate in cages. Although many in the USA on this forum are anti-substrate, in the UK and elsewhere it is common. Done right, its fine.
Sand is okay. HOwever its a pain in the butt to clean up. YOu have to remove and wash or replace it frequently. Some chameleons will purposefully or accidentally ingest it, and while a little is unlikely to hurt a lot could pose serious risk. i would recommend considering something else.