KMG’s suggestion for a humidifier is probably the way that I would go for a quick and inexpensive fix. I do use a smaller one in my daughter’s room at night, and it keeps her room right around 55%. Typically, my house is sitting somewhere in the low 40s so that’s a pretty good increase for just a little money. Sometimes during the winter when the heat sucks all my humidity out I'll move it into the snake room for a few hours during the day and it sorts my issue out for me.
Daski mentioned making some alterations to your HVAC, which is a great idea too if you want to help keep the humidity in your whole house at a higher level. As a matter of fact, Snake Discovery, who’s one of my favorite family-friendly youtubers, installed a system like this in their “zoo.” Instead of having to worry about individual enclosures they’re able to just control the humidity in their entire building from one panel.