We had an oil heater in DS room (until it leaked oil and smelt terrible) and he had no problem! He was wearing a wondersuit type thing (a kmart one) with a singlet underneath and in a sleeping bag (either polar fleece or a velour type one from Myer). He has flannelette sheets (with a sheepskin underneath) and a flannelette quilt thing his nana made, and if I think he'll need more warmth, a cot panel. I find if he gets too hot, he just wriggles out from underneath.