I did some homework...okay...I used Google...
Earlier in the thread I mentioned steel wool and there was a question about humidity. Haven't seen anything negative (so far) and one site recommended it for pins and needles in humid areas to keep them from rusting. Would it effect long term? No idea. One tip I did see was to put a heavy metal washer in the bottom of the cushion to give it some weight. Some sites are listed below if you are interested.
https://www.craftsy.com/quilting/art...hion-stuffing/
https://www.ehow.com/info_12002477_s...hion-with.html
https://jacquelynnesteves.com/what-s...y-pin-cushion/