Combat boots are always a yes! Wearing them with a dress will definitely help you achieve that “not fancy” look. If you wanted to wear a pair of Converse sneakers, that would also work. However, don’t afraid to rock the combat boots and dress look, I’m a huge fan of that. If you wore a varsity jacket too, that would be killer! Jean jackets are also an option.
Are you planning on wearing a maxi dress or something shorter? Let me know and I can make a photoset of possible jacket/dress/shoe combinations. :)