I actually put my growing boys (don’t tell them I told you this) to bed with one each and every night from November through February. They seem to find them soothing, and of course hot water bottles do warm the bed! I love mine at my feet mostly, but on my stomach too, occasionally.
And there are so many fun places to shop: look here for a general survey. Here’s one with little fish visible swimming. Here’s a cute one in the shape of a heart. Here and here you’ll find hand-knit hot water bottles covers that two crafty bloggers created. This sort of hot water bottle cover is adorable, but I’ve found that the fabric contains the heat on the wrong side of the bottle. Oh, and here, well… don’t even look at this one. It’s not at all spiritual. Forget I mentioned it.