Someone already mentioned sheets, but bedding in general. I spent 3 weeks in Vietnam in December and sleeping in comfy hotel beds revealed how lacking my situation at home was. When I got back, I purchased a new duvet, duvet cover, mattress topper, new pillows and cases, and a headboard (my bed was just a frame). The duvet is filled with wool and it’s been perfect. I live in Canada and the nights have been cold, but not one of them have I been cold in my bed. I even stopped using a flat sheet since the duvet is inside of a cover. It’s been the perfect balance. I’m never cold or sweaty.