Remove the old upholstery from chair seat and back; remove chair back insert. Sand the chair frame, wipe with a tack cloth to remove dust, prime, and paint in your preferred color of latex paint. A semigloss finish will make the finished chair easier to clean. Let dry.
Measure the chair seat width and length. Add several inches to each measurement; use these figures to cut out a muslin pattern. Drape the muslin over the chair seat. Cut slits so the fabric will fit around the back and arm supports. Pin darts at the front corners to check for fit; unpin.
Add upholstery batting to chair seat as necessary. Using the muslin pattern, cut out a wool blanket piece. Drape the wool piece over the seat. Pin darts at the front corners; stitch darts. Ease in fullness along sides and back. Fold under extra fabric around arm and back supports, clipping fabric as necessary. Trim all extra fabric to eliminate bulk. Staple fabric to the bottom of the chair seat frame.
Cut a wool blanket oval 1 inch larger than the chair back insert. Cut a second wool blanket oval the same size as the insert; set aside. Place the larger wool oval over the front of the insert; using carpet thread, stitch around the outside edge of the wool oval and gather it to fit snugly around the insert. Secure thread and gathers to back of the insert.
Cover buttons with print fabric, following instructions on the button kit. Use the covered buttons to tuft the chair back, securing them on the back with sew-through buttons. (If your chair had been tufted, use the existing holes. If it had not been tufted, drill holes where you want the buttons to go.) Glue or staple the insert into the chair back opening. Glue the smaller wool oval to the back of the insert. If using a fabric that will fray, glue cording or braid over the raw edge.
Using the muslin pattern, cut out print fabric for chair seat slipcover. Determine the desired length of ruffle drop, then measure around the chair seat and multiply the number by 2 for extra fullness. Using these measurements, cut a print piece for the ruffle, then cut the piece into three segments to accommodate the chair's arms. Hem bottom and ends of ruffle pieces. Cut enough bias strips of print fabric to cover piping cord. Sew the bias strips together end to end, then use the long strip to cover cord. Stitch piping to slipcover. Gather ruffle and stitch ruffle to piping. Cut and stitch four ties from print fabric. Stitch two ties at each back corner to attach the slipcover to chair back supports.