Human hair is primarily made of keratin and is usually somewhat oily (a result of the sebaceous glands lubrication to help the follicles grow out of their subepidermal sheathing). Although keratin also forms the basis of horn, claws and even fingernails, it is an organic protein that can serve as food for microorganisms. It has a long history in art, which ...
After asking around, I had suggestions for:
Poly fill and down seem suitable for very puffy jackets (source), but didn't fit my vision of this particular one - might be too puffy, plus the lining would have to be more complicated to keep it distributed evenly. Flannel and wool would be warm, but they have no fluff at all,...
One way to prevent displacement is by making sure the stuffing cannot move anywhere. If all basic shapes (limbs, head, torso, &c.) are separated from the others by an internal wall or membrane, you will prevent the filling from moving outside their limited volume.
Use pre-shaped filling
You can alternatively adapt the stuffing to ...
It seems, from casting about online, that the use of wool stuffing for refurbishing furniture cushions is somewhat outmoded, even for a restoration project such as yours where authenticity is desired. Other than several blogs mentioning wool when discussing the pros and cons of various cushion materials, especially those which are emphasizing natural ...
Arne and Carlos have a video on how to recycle little bits of leftover yarn and using it as stuffing: https://www.youtube.com/watch?v=kogj9fSNqv4
They demonstrated brushing small amounts of leftover yarn back and forth between two carders (big wire brushes) until the fibers came apart and softened and it all turned into a fluffy blob of soft material ...
Cotton Balls - try pulling them apart a little with your fingers to give them more volume & squish.
Old Pillows - cut open an old pillow you don't need for the fluff inside (which is more or less polyfill).
Other possibilities: Roving wool, bulky/super bulky yarn (loosely wound up), microbeads, beans (don't get them wet though!).
Polyfil. If you want puffy filling, go with polyfil. You've already used it; it's a great filling for a puffy jacket. Since you're using a bomber jacket pattern (by the way - the picture makes it look more like a letterman than a bomber?) typically there would be some degree of 'puff' to it.
My grandfather's bomber jacket - an actual bomber jacket, he was a ...