I use a humidifier. It also has an ioniser & it helps with my allergies.
I bought it when we had our last kittens.
It's a plug-in electrical thing.
But I also use plastic containers, which can be filled with water and hooked onto radiators, or placed near other heaters.
Some are specially made, but any container can work.
The water evaporates into the air because of the heat.
So you can buy expensive devices, or just use old containers.