Comfortable pre-assembled retrofitting systems. The modular systems consist of spring elements which suit to all bed sizes and also to bevels as they exist in beds of caravans and motorhomes. By clipping the elements together an orthopaedic base is formed which supports the body in both lateral and longitudinal alignment. The chambers are permeable to air and help a healthy sleeping climate without condensation. We recommend a mattress made of latex or cold-foam with a height of 10 cm.