I use fleece longies and gmd workhorses for nights and I have been really happy. I find that the fleece will hold the moisture in. not a ton, but it doesn't leak either.
I used wool for awhile. I thought it was cuter and could be used more than once. Fleece smells like pee in the morning. Wool airs out and doesn't smell.
But my DH ruined too many woolies by washing them as diaper laundry. I picked my marriage over cute pants!