Lite Line 400

I have the Panyam 450. It’s not the most ultralight option but it’s very comfortable. Have you also considered the Cumulus Lite Line 400? The comfort temperature is +2ºC but it’s lighter and apparently it can be pushed to 0°C.

I have a cumulus lite line and it's fantastic. Sadly got hit with a customs charge for it the week they were introduced post brexit.

Take a look at cumulus bags. They can do custom fill (up or down, “waterproof” different fabrics etc ) and custom sizing for it as well if you wish. Not cheap but personally I think they’re the best down bags on the market.