The waistband is the whole post and I learned it the bad way on a long flight in rigid trousers.
Feet and everything else swell noticeably over several hours, which is normal and which turns a merely snug waistband into the only thing you can think about. Anything with a partly elastic back, or a size that is comfortable when you are sitting rather than standing, fixes it entirely.
Test it by sitting down for ten minutes at home. Trousers that are fine standing and tight seated are the ones that ruin a flight.