Don't get me started on shoes. I wear a 6 in casual shoes and sandals, but a 5.5 in dress shoes. I have a medium wide foot, with narrow heels. And my left foot is almost half a size bigger than my right.
I consider myself lucky. I wore a size 5 until I had DS #1 and then my feet grew half a size. After DS #2 was born, I stretched that a little more.
My mom wore a size 4 her entire adult life. In the beginning, my dad owned a shoe factory and back in the day, the sample size was 4. By the 70's my dad was out of the shoe business and the sample size was 7. She had to go to Nordstroms to buy shoes for my wedding and often resorted to the kid's department. She was exactly five feet tall and never had trouble finding clothes back in the fifties, sixties, and through the seventies. After that, she had the same issues as me. I recently took her wedding dress out of the hermetically sealed box, as my DIL was going to use some of the lace. I could not believe how teeny her waist was. She must have weighed 85 pounds. Even I could not have fit in that dress. Yet, she had gorgeous clothes when I was little and didn't have trouble finding them.