I recently bought two hot water bottles as three of us were vying for the use of our one bottle. But I didn't have covers for them and there's no time to knit any.
Just then I noticed a big bag full of baby clothes ready to take to the op shop. I picked out two cute fleecy ones with feet. With appliques and ribbons etc they were never useful as babysuits; in fact I don't think Umi wore them. But they are great as hottie covers!
Just fill the hottie, pop into the suit, and do up the press studs over it. The neck of the bottle can stick out from the neck of the babysuit. I find size 00 fit perfectly!
It makes the whole family feel like they are cuddling up to a cute little baby at night.