A spring mattress with longitudinal strings comprising a plurality of interconnected coil springs (1) enclosed in covers (2) is described, wherein a plurality of such parallel strings are arranged side by side and interconnected by surface attachment between abutting surfaces. Furthermore, a slit is provided between at least two springs located adjacent to one another within the same string, which slit allows an increased interjacent separation distance (SA) to be formed between, said adjacent springs. Also described are a method and a device, respectively, for manufacturing a corresponding mattress.