In the video below I show you how to make a french mattress cushion. I used polyester for the filling, but you can also use foam flakes or spaghetti latex. Or simply a bit softer solid piece of foam . I left the edges as they are. But you can of course also make them thicker with extra dacron or you can scoop a little bit filling with your needle in the seams. And instead of a cross-stitch in the middle you can also place an upholstered button. I did the stitches on the edge with extra thick yarn or also called barbour yarn. I also did that with a different color. Why? So that the viewer can see it all well.
You can save yourself a lot of work and buy such a cushion at Ikea or so.
But doing it yourself is of course more fun and the advantage is that you can make them in all shapes and sizes.
Oh and for the explanation, turn on the subtitles at the bottom right of the video.