A couple of long sleeve travel shirts will cover most situations. Long sleeves can be rolled up to keep you cool, give protection from the Sun and from biting insects, whilst being breathable. In the cold, travel shirts offer an extra layer of insulation. For trips to malaria risk zones, you can buy treated clothing, like the Craghoppers Nosilife range, which kills biters on contact. Otherwise, you can simply treat your clothing yourself fabric treatment. Cotton shirts give the most comfort in the heat, polyester based are much quicker to dry. You might find one of each a useful combination!