What Elmer said. I don't have any advice about compression stockings, but I do know that you should get up and walk around the plane often (hourly when you're not sleeping), and do leg exercises when you're sitting. Drink plenty of water, which will help force you to get up (I hope you have an aisle seat!).

I googled for medical opinions on the Firefly device. Didn't find medical advice (admittedly I gave up rather quickly) but did find the review linked below. One point to note is that the battery is single use and good for approximately 30 hours, after which it must be replaced; this adds $$ to the initial cost.

https://www.gearpatrol.com/fitness/a42890391/firefly-recovery-review/

I share your concern about the stress of such long confinement. I like an aisle seat because it seems roomier, somehow.

There are exercises you can do in your seat in addition to a walkaround as often as you can. I sometimes stand up and stretch without leaving my seat area. I might look silly, but don't care.

You could ask your physician about something to ease your mind and any anxiety, relax your legs. (If you get something, try it out before being on a plane.) Be sure you have comfort items like travel pillow/blanket unless provided by the airline.

You could get some compression socks and wear them around for a day or two to see if you like them.

Needless to say, stay hydrated.

Hope you have a wonderful trip.

Why not just make sure to get up every two hours or so?

When you exercise a muscle, the blood vessels expand to allow more blood to that muscle. Other blood vessels constrict to help direct the blood. The general blood flow increases as well as the heart works harder. Whether the linked device accomplishes all that, I have no idea.

Aisle seat, stand often!

I wear compression socks when I travel. I prefer the Comrad brand. I use the ones with moderate compression. They provide sufficient compression without being too much.

https://www.comradsocks.com

"Why not just make sure to get up every two hours or so?"

Lol. Yes, eld, you may think that that helps, but it seems clear that you're not an RLS sufferer. Be thankful for that!

Show me the flight with passengers cruising the aisles at will. The Fasten Seatbelts sign will appear. You can stand at your seat a few times.

How long do you just sit when you're at home? In a car? You just need *some* movement. I'd do foot/ankle circles, some glute compressions, upper body movement. Compression stockings could help -- *light* compression.

DH and I eventually realized that the cost of sleeper seats was well worth it when we'd fly Chicago-Maui.

Now I will only plan to travel once the Transporter Room is a reality. Then I'll worry that my molecules will get mixed up in transit.