One of the reasons I prefer modular construction to the trendier shipping container housing is that the size of the module can be designed for people, rather than stuff. The Freedomky, from Czech architect Marek Štěpán, is a good example. It packs a comfortable 400 square foot one bedroom unit into a single box.
It is a very energy-efficient design that comes with a heat recovery ventilator and an air-to-air heat pump. All building materials are "ecologically benign." Photovoltaics and solar thermal hot water are also available.
It is a simple, straightforward plan.
You can actually walk around the double bed. The builders write:
A Freedomky is an artfully conceived home that prioritizes the efficient use of space, high quality, and low ecological impact. It provides a level of comfort suitable to your particular needs. It is less expensive than a traditional flat and designed to enable complete independence from utility networks.
It's only available in Europe; a shame, because it is a nicely done, simple design. More at Freedomky.