If you know how to sew (or glue) you can make your own chair pads or covered foam cushions. Make them to match your decor or recover old ones that are tattered. You can make a pillow using the same steps. In essence, you are making a fabric envelope that will hold your cushion. If your cushion is very thick, it may actually resemble a flat box of fabric (sides are wider). The goal is to make three sides, stuff it with contents, then stitch the rest closed.
Measure your foam piece. The instructions assume a square piece, but adjust for your particular foam item. Fold your fabric with the right sides together. Mark a square in chalk on the folded fabric according to your measurements, then add 2 inches all the way around for a cutting line. Cut out the square at the larger size and use straight pins to hold the two pieces of fabric together.
Sew three sides together along the chalked lines. Don't be afraid to give it a clean corner. For the fourth side you can sew the corners, but do not go more than 2 inches from the ends. Now you should have a pocket with three sewn sides, and the corners of the fourth side.
Trim your seams all the way around, not too close to your stitched line. Leave about 1 inch of fabric. To make the pocket have clean corners, however, snip the corner fabric closer to the edge, making sure not to cut the sewn line. Turn the fabric pocket right side out. On the fourth edge, use an iron to fold over the edge by about 1 inch, this is going to make sewing it closed easier.
Take your foam square, and wrap it entirely in batting. This will soften the cushion and make it last longer. Slide the entire envelope of fabric over your cushion. You won't have a lot of play to stitch it closed, but you should have enough. Using doubled heavy-duty thread, stitch the cushion closed. If you wish, sew in a zipper so you can take the cover off for cleaning.
To make the cushion decorative, add buttons or piping around the seams. Choose different fabrics for each side ... let your creativity be your guide. Follow this same process to cover a pillow.