Here are the recommendations on my humidistat:

-30℃, 15%
-25℃, 20%
-20℃, 25%
-10℃, 30%
-5℃, 35%
0℃, 40%

We have a humidifier that ties into the forced-air ducts of our heating system.

Also a little plug-in unit in the bedroom, which I like to crank up a couple hours before going to bed, then I put the fan on low for overnight so it's not too noisy. It is off the rest of the day so that condensation doesn't build up on the windows.