Do you sew? I have made a few "blanket -like bags" out of polar fleece for a friend. They open on the front with snaps . I have threatened to make her a snuggie too.

Leg warmers are your friend. polar fleece, knitted, store bought or homemade, indoors or out.

Found a link at amazon us for a heavy-duty wheelchair blanket to give the idea. https://www.amazon.com/XWSM-Waterproof-Fleece-Wheelchair-Blanket/dp/B08SK87SM9