I hate having to watch sick friends struggle.
A cat is the worst to deal with it seems because even vets usually say there is only "so much they can do."
I was not familiar with the term "doona" either, but only "so much you can do." Clean and sterilize it or replace it.
Good luck with your cat's troubles.
Mine is thirteen years old and I feel I have to watch her for signs of "Oh,NO!" all the time.