If anyone does wear them, make sure they're the right size - Mum's spare pair might not necessarily fit!
11 hours is about as long as any flight - any longer, and there will be refuelling stops, when you can get off and walk around. The other issue with very long fligths, is that you will probably sleep at least some of the time, which means a break in the recommended "get up and walk around" regime. If you're in an aisle seat, it's easy to get up, but equally, you might be woken by those in middle or window seats who need to get past you. Best long flights I've been on have been when I've been lucky enough to have 3 seats to myself, so can sleep flattish, if curled up. Many years ago, before diagnosis, very helpful steward on a Malaysian Airlines flight London / Australia, helped a group of us youngish travellers (we didn't know each other at the beginning) by supplying packs of cards and extra drinks - being near the service area was good in this example.