Have you had a look at the Alpkit bags?

PD600 has a comfort of -10, decent baffles and quality down for £230.

https://www.alpkit.com/products/pipedream-600

Some more info on sleeping bag ratings along with notes about reducing weight - https://www.backpackingnorth.com/ultral ... r-bedding/

Thanks! That's a good article. I'll have to look up some of the quilts mentioned (along with the Alpkit). I came across the ZPacks quilts which seem like they might be good, but the current exchange rate is making this sort of purchase much less of an 'impulse' buy!