A mattress wherein a plurality of independent yarn based fire barrier fabrics encases a plurality of distinct and unattached interior core structures. The plurality of interior core structures include at least a detached and internally flippable upper comfort layer assembly with a plurality of non-homogeneous foams or filling materials encased in a yarn-based fire barrier fabric and a lower, interiorly disposed support core structure with resilient filling materials encased in a yarn-based fire barrier fabric and a fabric cover. The detachable and internally flippable upper comfort layer assembly may be contained in a user accessible compartment that is fashioned into an outer cover assembly.