I'm putting together some kit for the possibility of an extended tour sometime in the future, which might involve autumn and winter, where the temps drop below freezing (but nothing truely extreme).
I'm looking at sleeping bags now (always a minefield, I know).
I'm considering taking two bags, a summer bag which weighs about 1kg and packs down to about 20x20 cm, and maybe a 2/3 season bag or straight 3 season bag. I've seen a 3 season bag which weighs about 1.5 kg and packs to about 25x20 cm. This means I'd have options of combining the bags or not, depending on weather.
I've also got a thermarest prolite to sleep on to keep the heat from escaping into the ground.

What I'm looking for really is an idea about the kinds of weight, pack size you hardy souls take when touring in coler weather, and if you take two bags instead of one.

Thanks