Vicks - Warm Mist Humidifier VWM845

We use humidifiers that work with real steam (Verdampfer?). For us, this works better than all the other stuff that have some "cool steam" or ionisers and other esoteric bells and whistles. We went through most of the others and came back to the verdampfer. Also, it is safe for our pets; they won't go near it. Also, if you have radiators in your flat, there are little containers that you can hang on them and fill with water. The radiators will heat the water up and it will slowly evaporate. That will help as well (and you can put a few drops of essential oils in them for a bit of a nice fragrace, if you like that kind of thing).

The brand is "Vicks", but it is a few years old now. I think, the ~same devices are also sold under another name or two,

I have a Vicks warm moisture humidifier, no need for distilled water, just need to clean out out the little heater portion every once in a while. As far as frosting up your windows, other than getting better windows, there are little kits that come with thin clear plastic sheeting that you can tape over your windows that will decrease heat loss. The Vicks humidifier I have is easy to clean, just one screw and unclip it. Hard water buildup has the consistency of chalk, so you could use a screw driver or butter knife to break it up and get it out.