A mattress assembly, comprising: a frame; a plunger matrix supported by the frame comprising a plurality of plungers suspended by a plunger support platform, wherein each plunger provides an independent point of support and the plunger matrix defines a support profile for a person lying on the mattress assembly; a top pad located above the plunger matrix; a cover over the plunger matrix and the top pad; wherein each plunger comprises: a pin guide removably captured within an aperture through the plunger support platform a pin slidably received within the pin guide comprising a flange located above the flange of the pin guide and a shaft extending from the flange through the guide body, a deformable head carried by the flange of the pin; a tension spring having a first end fixed to the guide body and a second end located below the guide body positioned to receive a bottom end of the pin shaft, wherein the spring is configured to resiliently stretch with downward motion of the pin with respect to the pin guide; and wherein the support profile comprises plungers organized into a plurality of zones in which the plungers of each zone are similarly configured while the plungers of different zones are configured differently to define a varying firmness characteristic of the support profile across the zones; characterised in that: the pin guide comprises a flange positioned above the plunger support platform, a guide body extending from the flange through the aperture, and each plunger further comprises a dampening device captured around the shaft of the pin between the flange of the pin and the flange of the pin guide, wherein the dampening device is configured to resiliently deform with downward motion of the pin with respect to the pin guide. a frame; a plunger matrix supported by the frame comprising a plurality of plungers suspended by a plunger support platform, wherein each plunger provides an independent point of support and the plunger matrix defines a support profile for a person lying on the mattress assembly; a top pad located above the plunger matrix; a cover over the plunger matrix and the top pad; a pin guide removably captured within an aperture through the plunger support platform a pin slidably received within the pin guide comprising a flange located above the flange of the pin guide and a shaft extending from the flange through the guide body, a deformable head carried by the flange of the pin; a tension spring having a first end fixed to the guide body and a second end located below the guide body positioned to receive a bottom end of the pin shaft, wherein the spring is configured to resiliently stretch with downward motion of the pin with respect to the pin guide; and wherein the support profile comprises plungers organized into a plurality of zones in which the plungers of each zone are similarly configured while the plungers of different zones are configured differently to define a varying firmness characteristic of the support profile across the zones; the pin guide comprises a flange positioned above the plunger support platform, a guide body extending from the flange through the aperture, and each plunger further comprises a dampening device captured around the shaft of the pin between the flange of the pin and the flange of the pin guide, wherein the dampening device is configured to resiliently deform with downward motion of the pin with respect to the pin guide.