Most of my stables have a rubber bed but these are cow mattresses, fine chopped rubber about 9" deep with a membrane over it. It feels like a water bed when you walk on it.
I still bed deeply because what I found is that if they are only given a 'splash' area, they pee and poop on that and then lie on it.
I found the horses were stinking of urine and it was taking me ages to get the muck off them - I was also throwing out all the splash area every day so, it was not economical to just do the splash area.
I bed deeply - with banks, I find the horses spend a lot of time lying down whereas without they don't so much.
Nothing as good as seeing a horse lying down in a nice deep bed.