I'll throw in some simple-to-make footers that I've finally arrived at, after many. many other types. Instructions for making them: get balsa wood at a hobby store, make cubes about 3/4" on a side (could be 1" instead), line one side (the bottom) with soft felt, glue a piece of 3/4" square hardboard to the other side (top), begin to drill a roughly 1/4" hole in the center of that hardboard, but only about 1/8" deep, and finally, epoxy in a 1/4" steel ball bearing. Obviously, all the dimensions could be changed--this is doubtless the smallest you'd want them.
It's simple enough to make a triple of these and give them a try. I make no claims for them, but the maker of Neuance Shelves liked a set of them that I sent to him to try. Not that he raved about them, but he did think they worked pretty well.