What kind of seat covers do you use? Do you have a link?
The ones I prefer are the disposable BugOff Bed Bug Seat Cover / Protectors, in white. They came in packs of 12 [each cover is individually wrapped] and were US$6.99 for the 12 the last time I bought them. Unfortunately they appear to no longer be sold and haven't been for some time [before Covid].
https://www.amazon.com/gp/product/B0057B13TO/
Given the above pricing, you will therefore understand why I am NOT happy with the current pricing for disposable ones...
The disposables are particularly good if you have multiple legs in each direction when flying, and if you don't have access to laundry at your destination.
For reusable, I have a NiceSeats seat cover:
https://niceseats.com/I like it, though the fabric is a little thicker/heavier than I expected, making it bulkier when folded up than I had hoped for. But it works.
And a GermFreeBee fleece cover:
https://www.germfreebee.com/This one I quite like and if you have access to laundry at your destination, it can double as a fleece blanket once you've washed it

The company also makes disposable ones [pack of 2 for $14.95] which I have NOT tried so can't speak to.
If you search
Amazon you will see plenty of options for disposable covers of varying design and quality. Most have popped up since Covid. And they are expensive, often just 1 or 2 for US$10 or $15 !!!
An even easier solution though... Many people in the food allergy community have long used a CRIB SIZE FITTED SHEET. Some use a twin size one, though that would be a little big. This works not just on planes, but theatres, buses, and other places one may have a need to cover seats. We've used our disposable covers above as well as the crib sheet trick to cover the chairs in hotel rooms, too.
A fitted crib sheet is about 52” long by 28” wide and 5”-8" thick depending on brand. Some will be a little longer or wider, too. IKEA sells inexpensive cotton ones,
Walmart and Amazon some nice inexpensive microfibre ones [including cute Disney prints], as well as cotton. There are many brands and options and price points.
Obviously the fitted crib sheet is best for when you have laundry access... Though with IKEAs being 2 for CA$14 they would be cheaper than many of the current raft of disposables !!!
Ziploc bags are your friend, and we generally travel with access to laundry facilities these days.
Hope this helps.
SW