Mattress for a bed system having a lying surface, - with a foam core which has a core top facing the lying surface and a core underside facing away from the lying surface, - with a lifting device, in particular a lying surface height adjustment device, for adjusting the height of at least one lying surface zone of the lying surface, wherein the respective lying surface zone extends in a longitudinal direction of the lying surface only over a part of the entire lying surface length of the lying surface and in a transverse direction of the lying surface extending transversely to the longitudinal direction of the lying surface over the entire lying surface width of the lying surface, - with a mattress cover which encloses the foam core and the lifting device and which has the lying surface, - wherein the lifting device comprises at least one hydraulic or pneumatic lifting unit, - wherein the lifting device has a control device which has at least one pump device for conveying a fluid and a valve device, - wherein the lifting device has a plurality of fluid lines for fluidically coupling the respective lifting unit to the control device, - wherein the lifting device has an actuating device for manual actuation of the lifting device, - wherein an actuation for raising the respective lying surface zone is effected by fluid being supplied to the respective lifting unit, - wherein an actuation for lowering the respective lying surface zone is effected by fluid being discharged from the respective lifting unit, - wherein at least one channel is formed in the foam core, in which at least one of the fluid lines is arranged, - wherein the respective channel is completely enclosed by the foam core in a channel cross-section, characterised in that - the foam core is divided on a side of the respective channel facing the adjacent longitudinal side edge of the foam core in such a way that two regions (70, 71) of the foam core bear against one another at a parting surface, - the foam core encloses the respective channel, in the circumferential direction of the channel, in an undivided manner from the parting surface to the parting surface. - with a foam core which has a core top facing the lying surface and a core underside facing away from the lying surface, - with a lifting device, in particular a lying surface height adjustment device, for adjusting the height of at least one lying surface zone of the lying surface, wherein the respective lying surface zone extends in a longitudinal direction of the lying surface only over a part of the entire lying surface length of the lying surface and in a transverse direction of the lying surface extending transversely to the longitudinal direction of the lying surface over the entire lying surface width of the lying surface, - with a mattress cover which encloses the foam core and the lifting device and which has the lying surface, - wherein the lifting device comprises at least one hydraulic or pneumatic lifting unit, - wherein the lifting device has a control device which has at least one pump device for conveying a fluid and a valve device, - wherein the lifting device has a plurality of fluid lines for fluidically coupling the respective lifting unit to the control device, - wherein the lifting device has an actuating device for manual actuation of the lifting device, - wherein an actuation for raising the respective lying surface zone is effected by fluid being supplied to the respective lifting unit, - wherein an actuation for lowering the respective lying surface zone is effected by fluid being discharged from the respective lifting unit, - wherein at least one channel is formed in the foam core, in which at least one of the fluid lines is arranged, - wherein the respective channel is completely enclosed by the foam core in a channel cross-section, characterised in that - the foam core is divided on a side of the respective channel facing the adjacent longitudinal side edge of the foam core in such a way that two regions (70, 71) of the foam core bear against one another at a parting surface, - the foam core encloses the respective channel, in the circumferential direction of the channel, in an undivided manner from the parting surface to the parting surface.