i wouldn't get hung up on a hunting brand for down, my down is sierra design and eddie bauer, all 800 fill
i wear down under thin jackets all the time
a thin, somewhat loose fitting jacket compresses it slightly, but even after losing a small amount of insulation ability, i think down is still the warmest thing out there per weight and compressibility
i have low body fat and get cold easily (smoked for like 20 years also)
i can wear an eddie bauer down jacket and vest over a thin base layer, then a windproof shirt, and then a fleece weight jacket on top....and be warm while motionless for hours in the 20 F range
make sure to get a loft over 700 and tumble on low or no heat with tennis balls once a week or so to get the down puffed back up
i think layers and building your own system is the way, i have 2 really heavy coat and bib sets, but they only get used when it is ridiculously cold for around here (0 F range), walking in and climbing with a heavy coat is miserable