Older dogs, or those with medical conditions such as arthritis or dysplasia that make it difficult for them to get in and out of bed, will benefit from a firm, supportive mattress. Loose dog-bed fill materials don't generally support painful joints, and orthopedic mattresses are expensive. However, you needn't compromise you pet's health to save money -- the things you need to make a good bed yourself generally cost no more than a lesser quality commercial bed.
Measuring and Making Patterns
Measure your dog's length, from head to base of tail, while he is stretched out asleep. To get a bed width measurement, wait until he curls up, then measure from front to back. Add 2 inches to each measurement to ensure enough space.
Purchase high-density or domed orthopedic foam to match the adjusted measurements, thick enough to provide firm support for your dog. A tiny dog can get by with a 4-inch-thick mattress, but for large or heavy dogs, buy 7-inch-thick foam or thicker. Optionally, for large dogs, use a good innerspring mattress designed for a baby crib.
Draw a rectangle the size of the mattress, plus 1 inch in each direction, on newspaper to make a pattern for the top and bottom pieces.
Draw two rectangular strips -- one, the length by depth of the mattress, the other one the width by the depth of the mattress for the side pieces. Add 1 inch to the measurements on each side of both rectangles. Example: If the mattress length and width are 20 inches by 5 inches, draw a rectangular pattern 21 inches by 6 inches.
Cutting and Sewing the Bed
Fold the heavy cloth in half, keeping the sides and bottom even, and lay out the pattern pieces. Pin the top/bottom pattern against one side of the doubled cloth, and pin the length and width pieces side-by-side next to it, ensuring the patterns do not run off the cloth at any point. By doubling the cloth you automatically cut two of each pattern piece -- the necessary number for the project.
Remove the paper patterns from the cloth and using a sewing machine with a #16 denim needle and heavy, matching thread, sew all the side pieces together into one long strip -- alternating the width and length pieces. Make sure all the right sides of the fabric are together and make 1/2-inch-wide seams where they join.
Sew the strips together at the ends with a 1/2-inch-wide seam -- right sides facing as before -- to make a loop of the side pieces.
Pin one of the top or bottom pieces to the side pieces by lining up one corner with the correct seam. Put the long sides of the top rectangle adjacent to the long side strips and the width of the rectangle adjacent to the short side strips -- with the seams between the strips as the corner points. Pin carefully to maintain 1/2-inch seam allowance all around and adjust the gathers at the corners to prevent bunching there.
Stitch the top to sides with 1/2-inch seam, removing pins as you go.
Repeat the last two steps for the bottom piece -- maintaining the 1/2-inch seam allowance -- but leave one short side open to insert the foam mattress.
Turn the mattress cover right side out and iron it to straighten out the seams, then insert the high-density or domed orthopedic foam or crib mattress. If the cover is tight and hard to get the mattress into, bend the mattress slightly before inserting, then open it up inside the cover and straighten the seams around it to fit.
Fold the seams under on the open end and sew that part shut by hand -- using the same matching thread and a heavy needle. Make stitches as inconspicuous as possible.