Break in your flats in under five minutes.
Step 1: Put on thick socks, and then your flats.
Step 2: Blow-dry your shoes around the tight sections for a few minutes.
Step 3: Keep your socks/flats on while it cools.
Step 4: Test them out, repeat process if you need them more stretched out.
That's only part of the hack. What you do is turn all the hangars in your wardrobe one direction. When you wear something, put it back with the hangar the opposite way.
After a set period of time, like a year or so, all the clothes that still have reversed hangars, all the clothes that you didn't wear in the year, give to goodwill or something.