Just go to Walmart and purchase an inexpensive humidifier,they have them year round in the pharmacy area,around $20. & up. I had that problem in the beginning in our sunroom,where I was growing my first ones, placed a humidifier close by them and a thermometer that also had a humidity gauge on it,around $4.97 at Home Depot,the gauge showed me just how the humidifier was helping and the plants response,also. I now have about 3 humidifiers out there because my collection has grown, 3 different plant stands w/ 3 humidifiers,1 close to each stand. I also use pebble trays under them,but I'm not always diligent about keeping enough water in their trays.
I think the humidifiers really help.