Berkeley Wellness has a list of tips for buying shoes that will be good for your feet, including:

• Have your feet measured. Sizes change, shoe shapes (“lasts”) vary, and your feet grow over the years. In particular, the front of the foot gets wider and longer as you age. Put your full weight on your foot as it’s being measured. Nearly everyone has one foot that’s larger than the other; choose the size that fits the larger one.
• Feet expand during the course of the day (because of friction, heat, use, and prolonged standing), so shop at the end of the day if you can, when foot swelling is greatest.
• When standing, there should be half an inch of space between your largest toe and the tip of the shoe, and your toes should have room to wiggle upward.
• Make sure that the area of the metatarsal joints (the widest part of your foot) fits comfortably in the widest part of the shoe. The shoe should bend where your foot bends.
• Never buy uncomfortable shoes with the idea of breaking them in: The shoes won’t change, but your feet may—for the worse.

More tips at the link. Go forth and shop happily!