The present invention relates to a variable-size bed (10) comprising a mattress core (16) and a base (14), which base is adapted to support at least a portion of the mattress core, wherein the mattress core and base have adjustable widths or lengths and each of the mattress core and base is changeable between an expanded state and a contracted state corresponding to an expanded state and a contracted state of the bed, respectively, and wherein the bed further comprises a cover means adapted to provide covering over the mattress core in both the expanded state and the contracted state of the bed. The present invention also relates to a vehicle comprising such a variable-size bed.