A lot of people use a slab of untreated wood, with a piece of linoleum (that your rabbit can’t chew) glued on the top. Because of sore hocks, I like to put bathroom mats and fleeces on, but if you want something more natural you can use straw or hay.
You can bond your bunnies. There are loads of forums on here about bonding, so you can search them up and you’ll find lots of helpful information.
I don’t know if this is what your asking, but in my litterbox I use about 1/2 inch of pine pellets (dust extracted), filled with fresh hay. I dump it, hose it out, and refill it every few days.
Your rabbit’s cage should be big enough (at LEAST) for the rabbit to hop across 3 times, stand on her/his hind legs and not touch the ceiling, and lay in any direction with out touching the cage edges.
I have 2 bonded bunnies, and they live in a customized x-pen that is about 8ftx5ft, and they get around 2 hours of free range time around my entire house and 2 hours around my bedroom each day. (Your rabbit should free range for AT LEAST 3-4 hours each day.)
Hope I helped!!! 