Pack stuff under your bedchair, it's stops cold air circulation, use an army blanket on top of your groundsheet, it stops the cold coming through. Get a twinned skin bivvy, the gap in between the two layers provides a thermal breathable barrier. Get a thermal all in one, all the supermarkets do them. Thermal layers, a decent bag, a decent bedchair cover, hats, gloves, thermal boots, water bottle, masturbate, don't buy one of those heaters, there dangerous and not cost efficient.