Tucked-in top sheet can provide a comfortable feeling of snugness that duvets cannot, as duvets are not usually large enough to tuck under the mattress. So if you love the appeal and comfort of a layering top sheets will allow a wider range of blanket choices besides duvets, such as quilts and coverlets.
Most bed sheet sets will come with a bottom sheet, a pillow case, and a flat top sheet and the fabric selections are endless possibilities of linen, cotton, silk, etc.