Method for manufacturing a mattress for a user, the mattress comprising a mattress core and inserts for various body zones of the user, comprising the following steps: - recording a three-dimensional image of the user; - determination of the desired deformation of the inserts as a function of the three-dimensional recording of the user in order that for a lying position of the user on the inserts, the position of his/her spinal column corresponds to the position of his/her spinal column in upright position; - selection from an inventory of inserts the inserts with the desired deformation characteristics; - positioning the selected inserts at the lying side of the mattress core characterised in that - for a given body zone of the user, three inserts are used, namely a left-, a middle- and a right-insert, - for a given body zone, the three inserts are positioned on the lying side of the mattress core as follows: - the middle-insert in the middle; - the left-insert at the left side of the middle-insert; - the right-insert at the right side of the middle-insert, and whereby - the desired deformation of each insert is determined also taking account of the lying position of the user on the insert concerned, namely as follows: - the left-insert for the left lying position; - the middle-insert for the belly or back lying position. - the right-insert for the right lying position; - the left and/or the right insert at its inner edge comprises a transition zone, the deformation characteristic whereof, expressed in hardness, is the average of the hardness of the left- resp. the right insert and the middle insert, and; - the middle insert at one or both of its sides comprises one, resp. two transition zone (s), the deformation characteristic whereof, expressed in hardness, is the average of the hardness of the middle and the left-, resp. the right insert. - recording a three-dimensional image of the user; - determination of the desired deformation of the inserts as a function of the three-dimensional recording of the user in order that for a lying position of the user on the inserts, the position of his/her spinal column corresponds to the position of his/her spinal column in upright position; - selection from an inventory of inserts the inserts with the desired deformation characteristics; - positioning the selected inserts at the lying side of the mattress core characterised in that - for a given body zone of the user, three inserts are used, namely a left-, a middle- and a right-insert, - for a given body zone, the three inserts are positioned on the lying side of the mattress core as follows: - the middle-insert in the middle; - the left-insert at the left side of the middle-insert; - the right-insert at the right side of the middle-insert, and whereby - the middle-insert in the middle; - the left-insert at the left side of the middle-insert; - the right-insert at the right side of the middle-insert, and whereby - the desired deformation of each insert is determined also taking account of the lying position of the user on the insert concerned, namely as follows: - the left-insert for the left lying position; - the middle-insert for the belly or back lying position. - the right-insert for the right lying position; - the left-insert for the left lying position; - the middle-insert for the belly or back lying position. - the right-insert for the right lying position; - the left and/or the right insert at its inner edge comprises a transition zone, the deformation characteristic whereof, expressed in hardness, is the average of the hardness of the left- resp. the right insert and the middle insert, and; - the middle insert at one or both of its sides comprises one, resp. two transition zone (s), the deformation characteristic whereof, expressed in hardness, is the average of the hardness of the middle and the left-, resp. the right insert.