A mattress-supporting base includes three mattress support portions, multiple crossbars and a baseboard. Each of the mattress support portions has a first end and a second end. The first end of each mattress support portion connects to the first ends of the other two mattress support portions, and the second end of each mattress support portion connects to the second ends of the other two mattress support portions. The first two mattress support portions have four sections that are pivotally connected by three hinges. The third and center mattress support portion has two sections that are pivotally connected. The components of the mattress-supporting base fit into a packing box having an inner width that is neither wider than about ten times the width of the mattress support portions plus about eight times the thickness of the baseboard, nor longer than about one half the length of the assembled mattress-supporting base.