It was time. The cover was icky to touch and the padding was pretty well gone. I did have a pattern from one of the Big 4 but it would have required too much work to alter it to the correct length. So I used the old cover as my pattern. The sewing pattern recommended 1/4" elastic and extra-wide bias tape for the edges.
That was too much work. The original, store bought cover, had cording caught in the stitching. Much easier. I edge-finished the cover on the serger and then zig-zagged over some worsted-weight cotton yard for the cording. It worked like a charm. I added some layers of cotton and polyester batting - scraps that were laying around for the new padding.