I didn't realise there was as a simple reason why I needed sugar in my coffee; the coffee I was using was not fresh, and that made it bitter. Supermarket coffee and coffee roasted at a roaster that is stored on a shelf (IE: not roasted fresh on demand) will be more bitter and require sugar compared roasted on demand fresh roasted coffee beans.
If you find that your coffee is still not naturally sweet enough for your taste preferences, there is one simple trick you can use to make your coffee even more naturally sweet; when you are extracting your coffee, cut your extraction short, so instead of a 25 or 30 second extraction, aim for a 15 second extraction. If you want a stronger coffee, just add a second shot! No bitter aftertaste, and no sugar.