There are two things that I use to make economy flight bearable

- Stand for 30 min, then sit for 30 min or so. You will be surprised by how much better you feel by the end of the flight. I just grab Kindle and read it standing in the isle on domestic or walk to the back of the plane on widebody international flights (usually there is space there).

- Use inflatable pillow like this one https://www.amazon.com/gp/product/B06WVR48SW. You will get much better sleep with it