Chicken stock would be fine. You could also throw in some barley or lentils or a soup mix for some extra body. I like putting pumpkin in as it tends to fall apart and make the 'juice' extra tasty. Corn is also fantastic for another flavour. I've been going crazy on veg soups now that's it's got cold here in Melb. I can't stand a cold lunch when the weather's cold. Tomorrow's soup will be lamb shank, veg and butter beans...