These cushions are the easiest to make, no zips to worry about. Basically you cut a strip of fabric the width of your cushion pad plus 3cm for seams. The length of the fabric strip is twice the size of the cushion pad plus and overlap of 8cm, plus a hem of 6 cm, and a hem of 3cm.
Firslty zig zag the long edges of the fabric, then hem the short edges by turning under a cm, then turning over the remaining hem allowance, the wide hem will be the one on show and where you stitch your buttons.
Fold the fabric right sides together, overlapping the ends as shown in the photo, the small hem should be on the top. Sew down the sides. Now turn right sides out and add your buttons. I’m making my own ceramic buttons so I will have to show you the finished cushions later.
Updated this post to show you the finished cushions with my ceramic buttons. I stitched press studs on the inside behind the buttons just to finish them off properly but if you have enough of an overlap you don’t really need to do this.