If you have a bench that needs a cushion (or a replacement cushion), you could buy one. Selection will probably be limited and you’ll pay a pretty penny. Or, you could make one yourself and choose your own fabrics and make it exactly the size you want. Sew4Home shares a tutorial showing how. Their bench cushion has piping around the edges and is tufted with large fabric covered buttons. Those details are optional, but they sure do give a finished look to your cushion. Go to Sew4Home for the tutorial.
[photo from Sew4Home]