Comfortable shoes. Shoes should basically selected based on comfort and secondarily on style.
Difficult. Unfortunately, it's best to "fit the shoe to the foot, rather than the foot to the shoe" flat feet often take up more space, necessitating a wider shoe. Stand on a piece of paper and trace your foot. This will give you an idea about how big your shoe should be to properly fit your foot. The orthopaedic foot and ankle society strongly opposes "cosmetic" foot surgery geared at shoe fitting.