Abstract: A mattress including a housing having a panel forming a base and a border connected to the panel, wherein the panel and border define a receptacle having a first end and a second end. The mattress further includes a spring assembly positioned on the panel and within the receptacle, wherein the spring assembly comprises a plurality of first and second coils arranged in rows extending continuously from the first end to the second end of the receptacle, wherein the first coils are different in size from the second coils; wherein groups of one or more of the first coils and groups of one or more of the second coils define at least three zones of firmness between the first end and the second end of the receptacle, wherein each of the first and second coils includes a first end and a second end; and wherein the first ends of the first and second coils are disposed adjacent the housing panel and lie in a first plane parallel to the housing panel.