Some people will use aspen,but I personally would avoid it because it isn't usually as comfy as paper substrate though even with paper you can get somewhat hard pieces though that isn't as bad as a sharp piece of wood which could cause serious damage to tiny eyes and such.
I would aim for Kaytee Clean and Cozy as Carefresh is extremely dusty.Clean and Cozy is a lot cheaper too,especially if you can get it from an alternative online retailer like Chewy.Drs Foster and Smith might have it cheaper too,and there are tons of really nice individual fruits,seeds,and nuts which can be very good for those with lots of small pets,birds,and some exotic pets as well from there
