If you plan on breeding, I would go with some type of newsprint/kraft paper/etc ... Mulch, Aspen, Sani-Chips are too often the cause of hemipenal infections on breeding males ... nothing worse than having a valued breeder male loose his mojo due to bedding.

Paper is cheap, plentiful, and when you clean it, it's 100% clean everytime!

Just my humble opinion of course.

-adam