of wire support members 88 supported on and attached to the cross slats 68 70 72 74 76 78 80 82 and 84 in this embodiment a top layer 63 is applied over the assembly 86 and a cover or ticking 90 is provided to form the exterior surface for the entire foundation 60 the top layer 63 is similar in construction and performance to the bottom layer 68 of the mattress 30 particularly the top layer 63 is designed to provide a rigid support surface for the mattress 30 with a firmness above 30 ild and specifically above 55 ild the one sided inner spring mattress 30 constructed according to the invention offers considerable advantages over prior art conventional two sided mattresses in terms of reducing the amount of permanent deflection of the sleeping surface due to undesirable compaction of padding materials because the mattress 30 essentially has a 50 percent reduction in padding due to the rigid bottom layer 38 the coil assembly 12 does not settle into and compact a lower padding layer as would happen with a two sided mattress of conventional construction having identical padding layers on both sides the addition of a rigid foundation beneath the one sided mattress 30 also provides additional support for the coil springs of the mattress 30 and thus helps further reduce sagging the one sided mattress 30.