I'm a big fan of lamb jackets. Not the orange waterproof kind but a rectangle of old sweatshirt or fleece jacket lining, with two T-shaped holes cut for the front legs. We use them on any small or weak lambs or those born on a freezing cold day and find it makes a tremendous difference to survivability - just takes the edge off the challenge of the first couple of days. I feed colostrum for a couple of days - even though the antibodies can't be absorbed that long it has additional energy elements that follow-on milk doesn't. Draught-free, dry accommodation is essential and a new Mama helps most of all.