Whenever possible, my birds have a grate in the bottom of the cage that prevents them from reaching whatever is in the very bottom, most often newspaper. If a cage's grate has spacing too big, I fasten 1/2 x 1 or 1/2 by 1/2 cage wire to the grate.

For babies that have trouble walking on the grating or birds that sleep on the cage bottom, I generally use one of the following:

A rubber sink mat with holes in it that can be easily removed and washed. Don't ask me why, but they usually don't chew on it.

Industrial floor matting, the kind made for floors that often get wet. It also can be easily removed for cleaning, and probably over half the poop and food falls thru the holes. Restaurant supply stores, some "wholesale" clubs, and some home improvement stores sell it in tile-like squares.

Care Fresh ™. Granted, it can cause problems if they eat much of it, but then nothing (except maybe the popcorn) is really safe if they eat any quantity of it. At least C.F. is nontoxic and biodegradable; if they eat a little bit of it it is broken down in the crop and passes harmlessly through the system. Note: Be careful of using Care Fresh in nestboxes, as it is very absorbent and sometimes causes low humidity problems.