I converted a second hand IKEA single bed into a pull out guest bed. When folded away it's the standard single bed and when extended its slightly larger than a king size
Clever conversion: create an office and guest bedroom in one | Financial Times
HEMNES White Daybed Frame with 3 Drawers - Popular - IKEA
UTÅKER Stackable bed with 2 mattresses, pine/Minnesund, Twin - IKEA