Baby or adult? Babies need more to ensure they grow properly. Adults are fine with less as long as they have proper shelter and a shallow water bowl that they actually use.
For adults I try to keep the humidity at 50% or a little higher during these colder spells. But if it drifts below that I just add more water and stir the substrate. Keep in mind I'm in the mid atlantic region so our natural humidity is higher than other regions.
For warmer seasons I like to get the humidity around 60%.