If you haven't already, you can also cover three sides of the aquarium with posterboard material, or black sheeting. It will hold the heat better for you. Then you may be able to ditch that lamp to help with humidity.

You can also try switching to cypress mulch if you have some good lawn and garden stores around. It should hold humidity a little better than the aspen. Make sure it's good clean stuff. No bugs.

Welcome to the addiction!