we used feel cold on camp ive learnt that no matter how hot the days are you can soon get very cold in the dark of night, we upgraded to 400gsm sleeping bags that have not felt too hot in the summer and we sleep on a foil quilted mat on the airbed that I purchased for a couple of quid of ebay, it reflects your body heat rather than loose it through the bed, its all about layers of clothing too, vest, tshirt, fleece onesie then just strip down if its too warm which is better than being too cold! :)
Those foiled emergency blankets! Under the bed/sleeping bag, and on top too, as heat rises. Also, wear socks to bed, with pjs tucked into them. Husband used to swear by thermal long johns when he was working onsite, only problem he had was when you get back in the car you get very hot.