This almost seems like an ID student project, but it's actually in production: The Lönneberga Stacking Bed, by German furniture brand Richard Lampert. It's a sofa that turns into two twin beds, using the simplest design possible.
In addition to the simplicity of the design, I like the little shelf that just hangs on the edge:
One downside is that here is no back and the bolster relies on gravity, meaning it must be against a wall in sofa mode. Another is that it presumably takes two people to perform the bed/sofa transformations. Other than that, the Lönneberga certainly lives up to the Richard Lampert motto: