If you want to keep it simple, we use ALFALFA pelets from the feed store.
It makes clean up e-z and simple, and alfalfa is a staple.
They also like to dig in it, we keep about 3 inches in the bottum of their vivs.
But the best thing is it's cheap, we pay $15.00 for a 50 lb bag and it last about 3 months.
But our vivs are 24x24x48 inches, one bag per viv.
Doug, Rose, Spazz & Lucky