You should try the bag in the store. That is the only way to be sure.
You are slightly longer when the body relaxes to sleep. Likely you will compress the down if you stretch out in the bag and lose heat.

Have you considered making a synthetic quilt using Climashield Apex insulation for the same temperature range around freezing and above? And for damp conditions in Norway?

I made one recently and it cost about one half the price of the NF bag you are looking at. And the sewing was simply stitching around the perimeter to hold the insulation and closing one end for a foot pocket. Then added snaps to close the top end around your neck to hold in heat.
It will weigh less than the NF bag at 24 ounces/680 grams and is easy to wash compared to down. It compresses well though not quite as small as a down quilt of similar size.

If you have a twin size down duvet/ quilt at home you can pin it in the shape of a the quilt I described to see what I am talking about.

Before making my Apex quilt I looked at commercial ones online. Here are some links to those:

http://www.outdoortrailgear.com/feat...r-top-blanket/
This one costs $100 US and claims a 30F temperature. It is from a one person US cottage manufacturer.

https://backpackinglight.com/forums/...-quilt-design/ Synthetic Quilt design on MYOG(Make Your Own Gear) section of BPL(Backpackijng Light) website.

Thru-Hiker Thru-Hiker provides All materials for making an Apex quilt for various temperature levels.

Prodigy - Lightweight Synthetic Camping Quilt Commercial company Enlightened Equipment makes a 30F Prodigy Quilt for $175US.