I wear a down jacket under my leather jacket. Are you talking from experience or only guessing regarding feather compressing. I have never had that problem. Set up this way the riding clothes I wear are very warm.
I ran a test last weekend. I tried wearing Sliders Kevlar armored pants against regular jeans with long under pants under them. The sliders were much better. I also used thin shock cord around my ankles.
I have a few of what they some times call a down sweater , what they are is what appears to be a nearly paper thin down jacket . I normally wear a large but in these I buy a medium , they fit snug , so snug that they look like they are to small for me . I use them as a layer usually around the freezing mark with a summer jacket over it , that way I can strip a layer off and on getting in and out of the truck and I seldom get over heated or cold . What I have found is that even the thinnest down garment can keep you warm if it fits snug to the body .
Yesterday it was zero here with a 30mph wind , I wore a modern 700 count down North Face bomber waist length jacket with hood . The jacket fits close to the body so nothing can enter , and it didn't . I was as warm as toast like I was sitting around the house on a summer day .
From what I've read on mountaineering sites , NOTHING can beat down for warmth . I bought a Ralph Lauren Polo down filled jacket 25 years ago and it still looks new , or it did when my son borrowed it 3 years ago LOL . If you buy a good down jacket and you take care of it there is no reason why it shouldn't last you 25 years , or the rest of your life . All that said , in order to get maximum performance from down it has to fit close to the body .
TheReaper!