My sister was on dialysis for several years and she was also very very cold. She had a quilt that covered her from below her chin to over her feet. She used to sit in a recliner type chair (this was in the 90"s so that may have changed). knowing the size of chair and the size of your Dad, (tall short big small) will help in making a quilt that will fit his specific purpose. Maybe taller than wider so it doesn't end up dragging on the floor on either side of his chair. I also suggest either fleece or flannel for the backing, they are more snuggley.
Just a thought and wishing you and your father all the best.