Abstract: It is disclosed foam mattresses or toppers, and methods of using them, comprising a top surface defining lateral deflective areas thanks to structural modifications of the foam comprising a plurality of slots, grooves, voids or channels. The invention (mattresses, toppers or methods) allows controlling postural alignment while providing ultra-low mattress-body interface pressures for all body areas regardless of recumbent position. The method comprises the step of providing into a core section of the mattress a plurality of structural modifications comprising slots, and/or voids, to form transversal deflective areas into the mattress. The invention is preferably achieved by CNC (Computer Numerical Control) cutting the structural modifications (channels, slots and voids) into the mattress foam which support each area of the body. It is also disclosed mattresses or toppers in which foam inserts are kept or removed from the channels to modulate the deflections on one or both sides of the mattress.