Di,
(earlier post went to moderation, look for it later)
More thoughts...
Another suggestions is to have someone help you put on T.E.D. or similar compression socks for the trip before you get on the plane, and also make sure you have very warm soft socks (don't forget them, really!)
A shawl isn't a bad idea either, definitely something to cover up with to keep warm.
We had a member who is no longer active on this forum, and the links to his website no longer work, but, he still has much good information within his actual posts on travel with a power wheelchair, I will add the link to his post, just know the links within his post are no longer active.
The best of luck to you! It sounds like you're embarking on the next chapter of your adventure otherwise known as Life.
Below is a link to one of Quadbliss's posts on travel with ALS, if you're interested, do a search of his other posts, he had many helpful and practical suggestions.
https://www.alsforums.com/forum/people-als-pals/1917-air-plane-travel.html