Ah, I am a frozen wasteland of a body, so my only variance in my all-season duvet is whether there’s one flannel blanket on top (summertime), two flannel blankets (spring/fall), or two flannel blankets and a wool blanket (wintertime). Nothing but a sheet would mean I’d be up all night shivering. But I also can’t have the blankets directly against my skin, because both flannel and wool are uncomfortable to me.