I was a bit suprised when I started looking at single duvets after cot ones, too. But then I did find a few places that do single 4 or 4.5 tog duvets. Try John Lewis online, for one, (http://www.johnlewis.com
) - there is a 4.5 tog single duvet for £8.
Or else, what I almost did (before I found a 4.5 tog one on a sale in our local department store ata bargain price!!) was to buy a 'seasons' one, where you get a 10 tog and a 4 tog toegther that you can use separately, and then clip together for super-warmth in the winter. And just use the 4 tog bit for now, and the heavier one when they get older, since presumably, there comes a point where they need more togs to be warm enough, just like an adult.
Its all a bit irrelevant for us, anyway, since DD is currently going hrough a phase of kicking off the duvet and removing her pjyamas (AND nappy!!) before going to sleep. So am wondering why I bothered