Washed and strained river sand. Its natural gritt too for the chickens. Just use a kitty.litter scoop and scoop it out everyday off poop boards and once a week in the run.
Pine shavings in the coop would be fine.
I'd look into lining the floor with linoleum, adding poop shelves that can easily be scraped off with a cheap putty knife, and possibly using sand in the coop. That way, you can spend a few minutes a day with a kitty litter scoop, or a shovel or trowel, put the waste into a bucket, toss the contents of the bucket into a pile with leaves and grass clippings, turn and water the pile once in a while, and give it a good 6 months to a year before using it in the garden. If you can, give your chickens access to the compost pile(s). They'll turn it over and get some extra nutrients. When you do your deep cleaning, the lino should make it easier to clean, and you should be able to wash, dry, and re-use the sand you remove from the coop to clean it out. A lot of work on the front and back ends since you'd have to haul the sand and shovel it in and out of the coop, I'd imagine.
The deep litter method might work well for you, too, which is what I'd probably do if we had 20 chickens and a larger coop.
For us, we only have 4 and we're using a tractor for the time being. The coop floor is lined with linoleum. No problems with the chicks slipping. We're using shredded paper as bedding since it's free and always available to us, and wheat straw in the nesting boxes since it's cheap and we almost always have a few bales on hand for other purposes.
My son and I spend about 5 minutes each morning removing the soiled clumps and putting it into a bucket that gets dumped onto a compost pile. We top off with new paper when needed and plan on replacing the bedding/straw and giving the whole coop a good wipe down once a week. Chicks are fine. Haven't noticed any smell beyond that normal chicken smell, and the slight sweetness of the straw, and we toss in a handful of mint leaves sometimes.
I did see somewhere that somebody used chopped cardboard for bedding, which has me intrigued.