Forget a double bag and go for 2 seperate square 3 season bags with left and right hand zips then zip them together, far bigger than any double, loads of space and much warmer. Vango's Wildernes XL's are great for this.
------------- Dont dream your life, live your dream, or just go down the pub !!
We used to take a duvet and I was sceptical about the double bag but the coleman came free with our tent and it's great. I get cold but he gets hot, he just unzips his side and lets in air while my zipped side doesn't let in any draft at all. We sleep better for it cos if he gets cold he just zips up his side and it's impossible for anyone to leave the other exposed. After all these years sharing a bed, I'd feel weird sleeping in my own bag, it'd be like having twin beds...which isn't for us ..yet!
we bought a wilderness sunncamp 250. It says it is 2-3 season but I had my doubts. But it was cheap enough and so i bought 2 large fleeces from matalan and made an outer sleeping pocket of the fleeces and then got two flannelette sheets and made an inner sleeping bag liner. I have never been so hot even at easter when we got close to freezing temps. Already we are talking about ditching the outer fleece envelope now it has marginally warmed up. It proved to me that insulation under as much as on top of you is important and especially layers. We used to sleep under a heavy 15 tog duvet but were often cold. That will never happen again. our sleeping system feels about half the thickness of the duvet we had but is at least twice as hot.
And the best bit, the bags are unusually 170cm wide so plenty of room cos I hate the restriction of a single sleeping bag but hate to share.
Claud