In reply to BRILLBRUM:
You might be able to get a repair from one of the outdoor companies, not sure if Rab would help or maybe Phd, Patagonia I think did repairs at the Kendal fest..
Have you considered having it professionally washed and relofted, might bring it back to life.
Not sure where you live but the Rab factory shop at Alfreton has some big discounts on new coats.
I personally wouldn't use a fashion jacket as a donor due to the down being of what I'd imagine being a different loft and quality.
Perhaps someone on here might have an old wrecked coat they can donate as a down sourse
Love the fact you're trying to prolong the life of the jacket.