Maybe just get more plants. They add humidity to a house because they respirate as part of photosynthesis. And add a fan as Gasrocks advised. It will also help keep the mildew at bay.
My daughter manages to keep her house at about 35% in the winter time with aquariums and terrariums. She doesn't have any fish, just plants. In the aquariums, water plants with snails and glass shrimp to keep the algae down. In the terrariums, orchids that like humidity such as Masdevallia and Restrepia. She also keeps sundews for small insect control (and they always have their feet in water). The humidity often drops to 0% here in the desert so keeping her house at 35% with just plants is pretty good.
I'm on my way to her house. I'll add photos later.
Daisy
