I don't follow the guidelines. In any case, the lowest temp they cite is 16 degrees, presumably 'cos Britons have central heating.
I have no heating in my kids' room and my son (11 months) is in a sleeveless bodysuit, a long legged, long sleeved bodysuit and a 2.5 tog Grobag.
In the Summer, he was hot and I always dressed him in less than the suggested clothing, but now he seems comfortable and is sleeping through the night!!!! Yeeahhhh!!!