I have no clue about this concept.....don't think I've ever heard of it.
I'd think you'd want the floor space to be big enough they could all sit side by side without piling,
and some extra room around the edge that is sheltered from any drafts.
Don't understand the "wool string pompom"......make sure its nothing they could get tangled in.
My concern, precisely. I've seen chicks get tangled in stringy stuff, and was lucky to be there when it happened. Mrs K, I would be inclined to use strips of wool felt instead of yard. it can't possible get looped around little necks. You can get it where they sell crafts supplies, and you can cut it into any width strips you desire. It's easily (hot) glued to the ceiling of your foam cooler.