Hi, I think what you are looking for is a fixed loft ladder or a space saving staircase, these are a little steeper and normally have what is known as paddle steps, this allows the tread to be wider at one side and narrower at the other, a straight custom made staircase will almost certainly require at least 2800mm in length, these space saver staircases take up around 1500-1600mm and are only around 500mm wide, there are many styles to choose from such as plain wooden to contemporary timber and metal, all very easy to install, building regulations do not exist because you are only accessing one room, another alternative would be a spiral staircase taking up about 1500x1500mm on the landing, I hope this helps and good luck.