Lightweight 2-in-1 laptops with 13.3-inch or 14-inch screens are widely available, with Dell and Lenovo, in particular, offering some compelling models. But if you want to maximise portability in a 12.5-inch form factor, your options are more limited. They do, however, include Fujitsu's compact, 360-degree rotating-screen Lifebook P728.
Fujitsu Tablet Lifebook P728 at ZDNet