Hello Warthog,

I am still trying to get my head around the dog / better half - warmth comments, I'm not 100% sure... but I'm going with the better half not being the doggie right?

Isolating the insulation is the solution, and there are two way that you can improve your current circumstances without resorting to a new sleeping bag.

1> Decent (raised) ground insulation Thermarests, inflatable mattresses etc
2> A Goretex bivi bag, that your sleeping bag goes inside all inside the tent.

Other ways include a waterproof ground sheet with a blanket on top of the ground sheet, underneath the tent base make sure that your flysheet overlaps the ground sheet.
If youre still battling, a blanket draped over the inner tent, underneath the flysheet, easier on A frame type tents

Oh and as for combining sleeping bags with double zippers this doesnt help to keep warm, the "hot thing" inside the sleeping bag with you helps to keep warm.

However I cant help feeling that both your better half and doggie may not like you as much if you continue in your current manner.

Cheers G

Linzi is right. In addition to my thermarest and down sleeping bag I used sometime my sheep skin under my sleeping bag to isolate from the cold ground. It did make a lot of difference.
Sheep sking is great stuff: during the day you ride on it, at night you can use as seat, pillow or to sleep!
And when it was really THAT cold I wrapped myself with a space blanket. Noisy when I moved, I looked like a Xmas cracker but it works great!

Some clarity is needed.

Normally, when camping, my girlfriend and I zip the two bags together to sleep. Up to -2 or 3 ish this has been toasty. I recognise that the best insulation is when you are in your own bag, but this was not necessary on that occassion. We sleep on Thermarests, and bike kit.

On ths night in question, I was camping alone, apart from our dog who came with me. I slept in my bag, atop some bike kit, and a well inflated thermarest. The tent was pitched on snow, on a footprint. It snbowed throughout the night and the tent was covered. I had though that might insulate too... The dog, luckily for her, was just curled up along side me on her sheepskin. I did not try to stuff her into my sleeping bag, although I considered at about 4 am!!

Since then I have also bought a closed cell foam mattress to go under the Thermarest, also... Thankfully it is now about 20-25 degrees!

I am thinking of buying a bvi bag too, but this is not a goretex one. I simply don't have the funds to pay £150, when a PVC one should be as protective and about a fifth of the price... For when I need it, Goretex is OTT.

Coming into overlanding from a mountaineering background I've just kind of carried over all the methods I've used previously.

Down is the only choice for lightness and low weight. Care is needed to keep the bag dry, but is relatively easy. Light condensation etc, if fine, but prolonged dampness is bad. Air the bag every chance you get.
For this reason do not use a pvc bivi bag inside the tent - emergencies only.
A RAB Survival Zone bivi bag is good for this, but will not insulate much. (not cheap either - but very small)

Get a bag with a neck baffle (elastic draw string at neck height) and hood. Uncomfortable the first time you use them, but incredibly effective. If you don't like the feeling of the hood over your head, wear a hat, lots of heat loss comes from the noggin.

All good bags are likely to be mummy shaped - reducing the volume of moving air in the bag increases the warmth. This is the idea behind the silk liner - also very worth while - adds extra warmth for virtually no weight (keeps the bag clean too). I bought a length of horrible coloured silk from a sari shop in Sheffield and sewed up two sides. Voila, silk liner for a fiver.

I've been using a Mountain Equipment Dragon Classic 800 for about 5 years now. - not the lightest bag, but cheap (relatively) and effective.
I bought mine form 'Magic Mountain' the Mountain Equipment factory outlet in Glossop, UK. Cost me about £50(!) They have a constantly changing stock, so keep trying them. They also have a massive summer and winter sale at the factory just down the road for two days a year - also worth trying if you're able to get to it...

Thermarest is excellent idea - should be all you need ground insulation wise.
Food before sleeping is also essential. As is keeping well hydrated. Keeps the blood thin and circulating.
If I'm cold before getting into my bag at night, e.g. just put up the tent, sweat starting to congeal on the skin - I run around for a while to warm up before getting into the bag.

At the end of the day one cold night will feel pretty cold whatever you do, a week of them and you start not to notice it!

Sorry for the long post - spent a large part of my life so far working in climbing/outdoor gear shops!

Personally, I hate narrow bags despite their supposed superior performance.