This has become a real problem for me in the last couple of years. Instead of 10M, now I seem to need 10.5W. Also the soles of my feet start hurting much faster, and I don’t know what kind of shoes I need.
That's unfortunate. Where in the foot does it hurt? I used to have pain in the toe knuckles (don't know the real name for it) and barefoot shoes really helped me. I don't know if it will help, since I'm not an expert, but it might be worth discussing with a doctor if you can't seem to find comfortable shoes and your size change with no explainable reason. Physiotherapy might also help if doctors can't figure it out, since they help strengthen the supporting muscles and tendons, giving better stability...