Unfortunately, one of the main restrictions we have on the equipment we purchase is cost, so I am trying to buy the best we can afford.
The sleeping bags that fitted most of the criteria were Vango Venom 300, which should cope with the climate, with a comfort rating of 0c to +25c, are quite light at 880gr and compress to 22 x 14cm. I found them online at a very reasonable price and tried mine out, as soon as it arrived it was unpacked, fluffed and contained me!
I was snug, but then, I was lying on the bedroom floor, fully clothed, on a warm evening on my Thermarest Prolite 3 Womens Regular self-inflating mat. Sad. I am very excitable!
I got David the same sleeping bag and his own mat, because he didn't already have one. His is perhaps a little better than mine, a Thermarest Prolite 4 Regular, but I've used mine backpacking before and I know I'm quite comfortable on it, so I'm not jealous.
Better not start any more research now, I mustn't spend everynight doing this when I have nearly 20 months to plan it!