Try going to a good shoe store and find a knowledgeable person there to correctly size your feet.

It is an eye opener. I did that when I got plantar faciaitis and the doctor suggested getting Mephisto shoes from the Walking Company since they gave a discount to his patients. The shoe guy was great. He really knew his stuff. I learned that I have been wearing the wrong sized shoes almost all my life. Every brand will vary as far as sizing goes and I find that my correct shoe size can vary by as much as 2-3 full shoe sizes depending on brand and type of shoe.

He told me that the trick is to buy the shoes that flex where your feet flex and not by the numerical size. That has made a huge difference for me. I hope that might help you.