W/o "quoting" your post, Tipi, to save redundancy, I'll further share how I managed the down, I actually collected the harvested down into 1-quart zip-locks, and went so far as to weigh it, in grams, distributing the grams proportional to the baffle sizes as they varied down the length of the bag' I know, totally anal, but I had the time.
But after distributing the down into the zip-locks, I'd make a slit on a baffle (inside of bag, of course), take my 1" PVC pipe and "stuff" it carefully with a zip-lock's down, put the end of the pipe into the slit, then "plunge" the down out with a piece of broom handle that happened to just fit inside of the PCV pipe nearly perfectly.
So bottom line to Tipi's OP, save those old down items! Especially the ones with good, high quality down.
I almost bought some down on Amazon once, it seemed reasonable in price, and was quoted as "800" or "850" fill. I can't seem to find that now, but here's some "750", if you believe it, $25 for 200 grams (about 7 ounces, that's a lot of down). 750 isn't bad down, again, if you believe it.
https://www.amazon.com/dp/B07H7RPSSG...jaz10cnVl&th=1