I need to get one of these for my 2 yo dd. Most of them seem to be 4, though john lewis has one that's 7. What's the usual tog rating to buy? At the moment she's in pyjama's with a doubled fleece blanket from ikea that she normally kicks off. Is a 4 the standard to go for, I know it works a bit different from adult tog ratings. Or would a 7 see her all the way through winter - do you switch to a warmer one in Jan if you have a 4?