A spring unit for a spring upholstered article such as a mattress or furniture includes a single length of wire defining a single length spring. The single length spring includes a plurality of adjacent coil springs which each have upper and lower coils with each coil spring being joined to adjacent coil springs by wire links which constitute extensions of at least one of the upper and lower coils. The single length spring is sheathed within a sleeve or envelope of cloth to define a sheathed single length spring. The sheathed single length spring is arranged to define adjacent segments of sheathed coil springs in which longitudinal axes of the coil springs in the adjacent segments are substantially parallel to one another. In addition, the upper coils of the coil springs in adjacent segments lye in a substantially common plane and the lower coils of the coil springs in adjacent segments lye in a substantially common plane.