Ya, aspen is great for burrowing but right now i am using repti bark, and my corn loves it, they can burrow it is a good source of humidity if you need it, and holds its heat well around 90 degrees and its an easy clean. But in the end i would rather go with aspen cause its cheaper and it holds their burrows nicely, and is an easy spot clean. But you go with whatever as long as its not sand, cedar, or pine.
90 is a bit high for corn snakes. Their hot spot should really be in the 83-85 range.