I did something similar for a changing table topper. I took a flannel backed tablecloth to make a pillow type topper for the changing table. Don't recall what I put inside, think it might have been a really thinned down old pillow. Because it was not very big and I wanted to maintain it's dampness resistance I did not even tie it. Then did a regular fabric or flannel cover that could be taken off and thrown in the washer so there was no need for DGS to lay directly on the plastic.