It is worth noting that “bed size” in the UK generally refers to mattress size. This is because mattresses have a standard size grading, whereas bed frames do not. Buy Signature Sleep Memory Foam 12 Inch Mattress, Twin: Mattresses – Amazon.com FREE DELIVERY possible on eligible purchases Make sure this fits by entering your model number.; The Signature Sleep Memoir 8 inch mattress is made with a 2″ top layer of comfortable Memoir Foam, followed by 6 inches of high density foam; this allows for the mattress to mold to the body’s natural shape for a comfortable night’s sleep Loft Bed Plans. Instructions for how to build a Loft Bed twin-sized standard height. This Loft Bed Plan measures 65 inches in height, by 42″ wide, by 81″ long with about 48 inches of clearance beneath. .