Modern mattress: Get a great night’s sleep with a Bonnell sprung memory foam mattress. Mattress depth: A sprung and memory foam layer, for a total depth of approximately 23cm. Layers: With a 13.5 gauge coil spring unit, plus a memory foam layer to mould to your body. Firmness: This mattress is single sided with a medium firmness, and is semi-orthopaedic. Cover material: Hypoallergenic, anti-bacterial with a micro-quilted top and orange border. Five sizes: Choose from small single, single, small double, double or king (see prices below).