Full grown ficus? like 7 ft? I've only seen them at nurseries and craigslist. At a nursery you are talking some cash as they have been grown by someone for years. I have had no luck getting any ficus for a while. I have been looking for several months.
Pothos are my favorite. Easy, cheap and fast growing. They show plenty of signs of dehydration before they die but I don't think there is such thing as too much water. They can be grown in just water if there is some nutrients (tap water usually has enough). Easy to propagate and is the most time tested for chams. And being a fast growing vine, my hunch is, they help with humidity more than most plants. I was able to get a nice big one at Lowe's for $10 or $12 and I placed it at the bottom of the cage and strong the vines to the top.
Umbrella plant (Schefflera Arboricola) is another favorite. Caution though, they are toxic to dogs and cats (maybe children? not sure). They can be a bit of a problem as they need to have their soil dry out between watering.
Here is a safe plants list... Note that just because they are safe, does not mean they can be grown under a single fluorescent and a heat bulb. Some are not concidered "house plants" because they need more light.
https://flchams.com/chameleon-safe-plant-list/
No matter what plant you choose, look up how to clean the plant's leaves of pesticides and fertilizers and re pot the plant with safe soil.