Plan the outfit around your shoes coming off, twice. Security, then again once you are up.
That means socks you are happy to walk to the toilet in, and shoes that go back on without sitting on the floor. It sounds trivial and it is the difference between taking them off and leaving them on for eleven hours because putting them back on is a production.
Half a size of room, as the post says. Feet swell measurably and a shoe that fits at departure will not at landing.