This three seater sofa converts into a double-bed, with storage underneath. Full product description here: http://www.ikea.com/gb/en/catalog/products/S89903190/
It's in the Christmas Sale and doesn't appear to be nation-wide. For example, it's available at the Nottingham and Manchester stores, but not Croydon or Wembley for us Londoners. Might be at some other branches, but I haven't sifted through the full list just yet.
Regular sale price is £200 but sign up for IKEA Family loyalty card for free and get 10% off all sale prices, so £180 :)