If you don't wear contacts because your eyes get dry easily, I really recommend Acuvue Oasys. My eye used to be so dry that the contact lenses popped out after an hour of wearing, and the pain, of course, was unbearable. Now I can even sleep with my contact lenses on.
I got lucky with my Coach frames because I purchased them from Coach and brought them to get my lenses, but you are better off going through an optometrist because not all frames can get prescription lenses.
I've purchased sunglasses at Nordstrom Rack and Neiman Marcus Last Call and had them fitted with prescription lenses at an optometrist. Just avoid sunglasses with huge lenses and I think you should be fine.