Goose Down is one of Dulux's most useful soft green-greys, and the trick with it is restraint. It's a quiet colour, so let it be quiet — run it across every wall, same colour throughout, and let it do the job of an envelope rather than a feature.
The single most important decision is your woodwork. Don't reach for a cool brilliant white — it'll throw the green undertone in Goose Down into sharp relief and make it look slightly sickly. Go for a warmer white instead, something with a touch of cream or stone to it. That softness keeps the green reading as gentle rather than acidic.
For accents, ground the scheme with depth. Deeper olive and khaki tones in your soft furnishings sit beautifully against Goose Down — they share its green DNA but bring the weight the walls deliberately lack. Paint & Paper Library Blue Blood (LRV 16.4) is a cracking choice for a feature piece or a smaller adjoining space, and Mylands Cigar BH.20 (LRV 11.8) brings a rich, smoky depth that reads almost as a neutral against the green-grey. Both anchor the room without fighting the walls.
If you want a lift rather than a contrast, Dulux Almost Pistachio (LRV 80.3) is in the same family but far lighter — ideal above a dado or as a ceiling tone if you want the green to carry upward gently. Goose Down works especially well below a dado with a slightly lighter stone white above; it gives a traditional, settled feel.
Keep your metals warm and aged — antique brass or aged bronze, never chrome or polished nickel, which will look cold and clinical against the warmth you're building.
Practical tip: sample Goose Down on more than one wall, because its undertone shifts noticeably between a north-facing and south-facing aspect. In poor light it can drift grey; in good light the green comes forward. Live with it for a couple of days before you commit the woodwork colour.