Getting myself a humidifier for my bedroom and my voice studios has been the best investment of my life. The two I like the most is this cool mist humidifier by Pure Enrichment for around $40 and this warm mist one by Vicks for $35. One uses sonic vibrations to create water vapor- the other steam. Both methods add water to the air, which raises its humidity, something I measure with this hygrometer.
Our vocal cords are very sensitive to moisture; the drier the air, the drier your feel your voice is, regardless of how well you are hydrated. I always run my humidifier in my voice studio as I teach, and at my bedside when I sleep. I even have a travel humidifier I use in my car and when I travel. The difference in my singing has been tangible; I wake up every morning with no dry mouth, ready to warm up and sing. My voice does not get fatigued on long teaching days. Long car rides? I often need to drive from Maine to Massachusetts to perform, coach or take lessons and the dry car air used to be an issues. No longer!
Invest in a humidifier- you won't regret it!