your question is about a down jacket, but let me sidetrack to down sleeping bags to make a point. You can buy all the down you want in a bag, but if the inner liner is slick and smooth, it still feels cold and you must sleep in long underwear and dry socks. After all, YOU are warming the bag up, not the other way around.
Same for the coat. So is the problem with your down coat not enough other warm layer under it, or not enough wind stoppage layer on the outside? If the latter is a problem, just put your loose fitting raincoat over the down.
sorry. you may already know all of this.
