Minus 5°C is about the coldest night you can expect on most mid-level treks, though it might dip lower. Both the Systems shown below will cope with this temperature with something to spare. They are based on the well-proven Minim 400 sleeping bag, a superb lightweight which gives -5°C performance at just 670g in its standard form and at an extraordinary 585g for the K model.
The extra warmth in 'System 1' comes from Minimus clothing, a highly practical and flexible choice. In 'System 2' the Filler bag is used as the simplest lightest way to add 10°C to the performance of the Minim 400.