Seat foam?

Bare bench bottom seat frame as the example.

3" burlap from bottom front edge to rear edge, also across from bottom left to bottom right.
Hog ring on ends only.

Then I wrapped it in the full burlap.
Then I hog ringed a skinny piece of thickish felt around the upper edge, this keeps the edge of the metal seat frame from wearing through the cover.
Then the foam on the top, only.
Then the muslin, then the cover.

Don't over do it with foam, just enough, the covers, especially if new, have some cushion in them, although a small amount.

If your original foam has the small wire embedded in it, do what you can to keep it.