Turn sweater inside out and sew across chest eliminating any sleeves and shoulder shaping. Use a low bulk seam finish to prevent fraying or raveling. Turn right side out. Add comfort material to inside. Even out material and pad as needed.
Roll or pin as for quilting and begin securing layers with small to medium stitch length freehand or pattern quilting. Secure padding and quilt through and next to additional padding.
Sew hems or bottom edges together. On many sweaters, the stretchy bottom treatment (cuff material) can remain. Just sew close to the edge.
Fasten off all stitching with backstitches and tie or apply seam sealer (Fray check). Check carefully for any remaining pins.