Hi, Baby-Daisy.
Cardboard is safe, but try to keep it plain, rather than boxes with a lot of ink and designs on it. A great chew toy that is safely made with soy based ink is a yellow pages. They love to chew, pull and shred them.
My bunny won’t walk on floors either. You can get an area rug that’s not expensive, ie. $20ish for 4’x5′ that your bunny might like to walk on. Or a long runner to go down hallways or from cage into the room. Check out our info. section for habitat tips, diet and behavior info.
Important: NEVER leave your dog and bunny alone together unsupervised. A Ch. can snap at a bunny suddenly and do some serious damage. They really should not be together much, so be prepared to separate them fast and watch/listen for warning signs from both bunny and dog, such as growling, squinting eyes, thumping feet, flattened ears, and separate them before either takes a bite or swipe with a paw.