I initially used a room size humidifier for the room I keep my violin in (I keep my violin out, too), along with a digital thermometer/hygrometer.  This Honeywell (1/2 gallon) is the one I used (there’s a 1 gallon one as well that works just as well).

Honeywell HUL520W Mistmate Cool Mist Humidifier

AcuRite 00613 Humidity Monitor with Indoor Thermometer

I have dry eye issues, & so I moved on to a larger humidifier that would work throughout the house.  I was skeptical that this one would work, but I’ve been using it for 3 years now, & I’m happy with it (was on sale when I bought it—costs a little more now). 

AIRCARE H12-400HB 4-Speed Whole-House Console-Style Evaporative Humidifier

I’m in Central Georgia, so I’m sure it doesn’t have to work as hard as it would up north.  I’ve got a ~2000 sq ft house, 1 story, with a couple rooms with elevated ceilings, & it gets the job done.  When humidity is low, I’ll keep it set at 45%, & it keeps rooms throughout the house at 39-42%.

I would also mention using a bacteria treatment for the water if you use a humidifier.  Don’t need to use much, so bottle lasts a while.  I use this one:

Essick Air 1970 Humidifier, 1-Quart Bacteriostatic Treatment