pothos are easy. almost impossible to kill. almost. ferns are pretty much autopilot plants. just remember that most ferns WILL grow huge if you don't keep them under control. i have a soft spot for prayer plants. i forget the species name, but a prayer plant was the first plant my mom gave me to grow when i was but a wee lad. diffenbachia as well. diff's will also grow huge, so trimming will eventually be required. these are all easily purchased at big box stores. depending on your locale, some places still have some nice plants in their garden centers, even at this time of year.

you can also use some bonsai plants. however, do research on these first. very important because some bonsai plants are of the pine family and they would only rot and die in a humid environment. i also believe pine is toxic to some frogs? but there are bonsai plants like ficus benjamina (which grow to 100+ feet in the rainforest) that can be trained to stay within the confines of a vivarium.

remember that orchids are cyclic plants. they bloom in cycles. they flower, then go dormant for a bit, then bloom again. my guess is you are growing phaelenopsis orchids and they are at the end of their bloom. just be patient, water it once a week and it will bloom again