In reply to cf:
Patagonia Puff Jacket. £130, great hood. Synthetic but light and compresses well. All you need.
Down is not good if there's any danger of it getting wet imho.
As for getting a waterproof down jacket, fair enough if you've got money to burn but if you can't air it, its true that over time body moisture will tend to reduce the down's loft.
Just get a Puff Jacket.