Hi, My name isXXXXX you for using Just Answer. I am another expert with some additional information regarding your concern.
You should look into purchasing some TED hose before your trip. These are tight fitting socks that go to your knees that puts pressure on your legs to keep clots from forming and can also help with swelling. I highly suggest you get these.
You should be able to purchase these at your local medical supply store, but if you can get your doctor to write a prescription for them a lot of time insurance will pay some if not fully for them.
While sitting on the plane, move your feet up and down (ankle pumps) and lift your feet slightly off the floor and move your ankle around in circles or for fun you can write the alphabet with your feet, anything to keep them moving and the blood flowing. This in combination with the TED hose should keep your swelling and chance of developing a clot to a minimum.
I hope you have a wonderful trip. If you have any further questions please let me know. Have a good day.