Substrate For Red Tail Boa

[the_flaxseed]

I have my new boa in a melamine enclosure and have been using aspen, but am having a hard time keep humidity up above 60% for more than a couple hours. I am considering switching to cypress mulch, but was wondering if it would be a bad idea to still keep some aspen in the enclosure for my red tail to burrow under (she loves doing this despite having multiple hides available). My concern is that the aspen could mold with the cypress mulch around. Is there another moist substrate that would work to keep the environment humid and still allow my boa to burrow?

Also, I got forest floor cypress mulch from zoomed. I've heard various concerns about it containing woodmites. Anyone have experience with this bedding that can comment on this?

Much appreciated, guys. Here's a picture of my new baby.