How can I make cushions for a porch swing?

Measure the seating area. Buy or make cushions or foam. To make no sew covers, use heavy duty Velcro, easy to remove and launder when needed.

This might be helpful: https://www.hometalk.com/diy/outdoor/decor/porch-swing-update-upholsterd-seat-30691434

A More Comfortable Porch Swing Seat

Check out your local stores for outdoor cushions. I found one for a window seat that was a nice thick cushion and just the right size. Best selection is now, and there are sales.

You can get some upholstery foam and cut it to size, then stitch some fabric together to cover the foam.

Got mine at Wal-Mart on sale...had pillows to match.