Honestly, if you need to ask here, then you aren't prepared to start breeding feeder mice anytime soon. Especially if you need to ask a question as simple as bedding, which is rodent keeping 101, it doesn't even tap into the breeding portion of it.
I'd actually recommend joining a forum dedicated to herps (reptiles). Do not find a forum dedicated to mice. Why? Herpers are used to feeder mice being fed to their animals, and know how to properly raised the mice in the
most humane and nutritious manner. A mouse forum is almost exclusively for pet keepers, and they will tear you apart for even thinking their tiny furry delights could be a meal for a corn snake.
Research general mouse care would be an excellent start. Then research breeding.
I can help you with bedding.
Use only aspen shavings, corn cob, or paper based beddings. Cedar or pine is awful for little rodent lungs (
in this article in particular, pay attention to pup mortality rates when raised on cedar versus aspen or corn cob bedding).. The powerful aromatic oils in pine or cedar irritate their respiratory system, making them more prone to respiratory infections. Think about how a rodent's body posture is. Where is their nose and mouth? Directly at bedding level, and they can't escape it.
I've never bred any rodents, I've only kept them as pets. I've also kept ball pythons. Though I fed frozen/thawed rats to my snakes, which were easy and cheap to buy in bulk and keep in the freezer.