I'm also looking for extra cover, since I have a long flight (11 hours) scheduled next month and have no experience in changing diapers on an airplane. I usually wear skirts and thights, they conceal the bulge but are not very convenient in smaller stalls when changing (really, that turns into a sort of a slapstick-situation, standing in a ballet position witch the tights around my ankles and holding the skirt up under my chin...soooo charming).
So I think I'll wear a thicker diaper than usual and use a cover just to be sure (and try to change anyways). I was thinking about buying this one from a french brand:
https://www.sanygia.com/en/culottes-sli ... nfort.html they seem perfect for use over the waistbelted diapers. I don't mind if I have to change both the diaper and the cover, I have a waterproof pouch to put the damp cover in if necessary
I hope your choice works well for you!