Wool fits all of your criteria. However wool does have very specific washing requirements. If you can get washable wool in the UK, I would go with wool. You also have to watch your distance. Most wool battings I have worked with require minimum quilting distance of 4". You definitely want a bonded wool to reduce the risk of bearding. Also you really have zero control over the durability aspect if the intended recipients don't take proper care of the quilt it won't last no matter how well constructed. Oops just reread your post and you say wool is out of the question. I would go with Poly but it isn't exactly considered sustainable.
It should fit all your other criteria.
Last edited by feline fanatic; 04-22-2019 at 05:53 AM.