In reply to elliot.baker:
My wife is not the greatest fan of camping and certainly wouldn't be happy with my ThermaRest ProLite - probably get on well with your g/f!
So I bought a Vango Comfort 5 double, which is very comfortable and can be got online for much less than the current £80 rrp. In fact, we now have 2, as I picked up a 2nd one on eBay for a bargain price for the kids - I just need to stop the 3-year old using it as a trampoline.
They are, however, a bit of a struggle to get back in the bag compared to the ProLite. They also do a 7.5cm version and a 10cm one, which must be a beast to re-pack and will probably take up 1/2 the car.
GoOutdoors have an Outwell 5cm double one on sale for £35 at the moment, which, in my opinion, would be a far better option than camp beds.
I've never taken normal bed sheets or duvets, but I know people that have taken a duvet on top of a thin sleeping bag. Thermarest, for 1, do dedicated sheets to slip on their mats - I'm sure they'd fit others.
My wife was none too impressed that I bought her this bag for Christmas one year, but has used it and finds it very warm, it even has fleece lined toes -
http://www.cotswoldoutdoor.com/vango-womens-stratos-250-sleeping-bag-d22321...
I have given serious thought to getting a double sleeping bag - we'll see how much we get out camping.
Good call on the hot water bottle. Dressing gown useful for trips to wash blocks. Take the biggest tent you have - girls like lots of space and headroom.
Be prepared to upgrade her if the weather's grim - my first attempted camping trip with my then new-ish girlfriend (now wife) ended up in a B&B for 2 nights due to high winds and rain!
Post edited at 13:00