A mattress customisable for at least one user comprising: - a main body with a sheet-like shape and which defines a supporting surface designed to support at least one user lying along a longitudinal dimension of the main body, the main body comprising at least one layer made of porous and/or soft material and having, along the longitudinal dimension, at least one series of upper channels and at least one series of lower channels offset relative to the upper channels, each of the series of channels (4a, 4b) extending along a transversal distance from one longitudinal side to an opposite longitudinal side of the main body and being designed to house respective slats in such a way as to define different configurations of the mattress as a function of physical characteristics of at least one user, and - a textile covering defining a containment space of shape and dimensions similar to the main body and designed to cover the main body, the textile covering being equipped with reversible perimeter closing means, positioned in at least one lateral portion of the textile covering corresponding to a respective longitudinal side, and designed to define a closed configuration, wherein the textile covering completely encloses the main body, and an open configuration wherein the lateral portion of textile covering is far from the longitudinal side in such a way that the channels (4a, 4b) can be reached in such a way as to extract and/or insert the slats in the respective channels (4a, 4b), wherein the reversible perimeter closing means are made in the form of a perimeter hinge positioned in the lateral portion of the textile covering in such a way as to be placed over three perimeter sides of the longitudinal side, said mattress further comprises at least a slat having at least one curvilinear portion defining a convex portion facing towards the supporting surface of the mattress and at least two rectilinear portions positioned in respective ends of the curvilinear portion, the slat being inserted in a respective upper channel or a respective lower channel as a function of physical characteristics of at least one user, the rectilinear portions having an overall length of at least a third of the longitudinal extension of the curvilinear portion. - a main body with a sheet-like shape and which defines a supporting surface designed to support at least one user lying along a longitudinal dimension of the main body, the main body comprising at least one layer made of porous and/or soft material and having, along the longitudinal dimension, at least one series of upper channels and at least one series of lower channels offset relative to the upper channels, each of the series of channels (4a, 4b) extending along a transversal distance from one longitudinal side to an opposite longitudinal side of the main body and being designed to house respective slats in such a way as to define different configurations of the mattress as a function of physical characteristics of at least one user, and - a textile covering defining a containment space of shape and dimensions similar to the main body and designed to cover the main body, the textile covering being equipped with reversible perimeter closing means, positioned in at least one lateral portion of the textile covering corresponding to a respective longitudinal side, and designed to define a closed configuration, wherein the textile covering completely encloses the main body, and an open configuration wherein the lateral portion of textile covering is far from the longitudinal side in such a way that the channels (4a, 4b) can be reached in such a way as to extract and/or insert the slats in the respective channels (4a, 4b), wherein the reversible perimeter closing means are made in the form of a perimeter hinge positioned in the lateral portion of the textile covering in such a way as to be placed over three perimeter sides of the longitudinal side, said mattress further comprises at least a slat having at least one curvilinear portion defining a convex portion facing towards the supporting surface of the mattress and at least two rectilinear portions positioned in respective ends of the curvilinear portion, the slat being inserted in a respective upper channel or a respective lower channel as a function of physical characteristics of at least one user, the rectilinear portions having an overall length of at least a third of the longitudinal extension of the curvilinear portion.