Varicose Veins & Spider Veins

tl; dr: I definitely think that a pod-like lay-flat seat would help with both giving you extra space in the name of COVID protection and also with your varicose veins. You didn't say where you need to travel to but there are many different iterations of first/business class seats so please be careful when selecting your airline and your seat! Always consult seatguru as you book or call the airline to confirm if they don't have a picture. Also, double check a week before your trip to make sure there hasn't been an aircraft swap.

The lay flat seats (that turn into a bed) - are the ones you often see from SFO to Asia and Europe and to major hubs on the east coast. The big airlines all have their versions of them but the nicest one is JetBlue Mint. With a few exceptions, like Singapore Airlines and some versions of Air France, you can expect these seats in *both* business class and first class (you do not necessarily need to spend the extra money to buy a "first class" seat when business class will suffice). You can still sit up but also easily elevate your legs with your footrest. When it's time to sleep, you can also figure out how to "cradle yourself" so that your legs are elevated. You may not be completely flat (like a bed) if you need your legs elevated but it will be worlds more comfortable than an economy seat. 

FYI: A regular domestic first class-type seat that reclines but doesn't go flat wouldn't be as effective as many of them do not even have a foot rest so I would not spend my money on those seats. You're better off getting an economy seat with extra space and putting a suitcase underneath the seat in front you to prop your legs up on. Safe travels!

Yes check if that flight has a flat bed. It makes a huge difference! For Covid risk take wipes to clean the bathroom before abs after use. That is the biggest risk as planes have hepa filters so the air is clean. 

One suggestion I have for the swelling is to get into a pool as soon as possible after you arrive. The pressure of the water helps your body return to "normal." I always do this in both directions when I fly, and I try to get into deep water every other day, especially when I'm traveling. I haven't tried flying first class. Train travel (sleeper car) was much better than flying but I'm assuming that you don't have the time for that.