I, too, am a former Diet Coke addict. Aside – when I had to give up caffeine, I discovered just how toxic Aspartame can be. It gave me horrible headaches. I guess having it in Diet Coke and in my coffee had been cancelling out the headache due to the caffeine.
When I feel the need for flavor, I drink fruit juice. Watch the calorie content, but juices are more filling than either water or Diet Coke, and so I find I don’t overdo on them (which it is possible to do because of the natural sugars they contain). Keep an eye out for added sugar.