I remember when I was a child: my grandparents used a very simple humidifier attached to the heating in each room [1]; I'm not sure how effective these are, but I guess they don't require any real maintenance. ;)

[1] http://bilder.zuhause.de/b/66/73/47/12/id_66734712/tid_da/sc...

While they're no longer sold in America, this Zojirushi warm steam design https://www.amazon.com/gp/product/B000PVXOX4/ requires very little in the way of cleaning and maintenance, just add some citric acid to the water and run its clean cycle when scale deposits get thick enough. Mine is still going strong after 7 winters.

I wouldn't, however, be inclined to buy an ultrasonic model like they're selling, you're depending on its filter way too much to keep dissolved solids and bacteria out of the air.