I wear ankle boots with suits all the time. Like shoes, they vary in respect to formality. I have a pair of single leather soled Banbury boots, from Edward Green, that I would wear with any suit in my wardrobe. Conversely, the Alden boots I have are much chunkier. Double soled, bigger lasts. They dont look right to my minds eye with thinner wieght suits. They look great with heavy tweeds though.