summer lightweight sleeping bag, winter low temp sleeping bag - what could be simpler?
a quick tip I learnt from my grandfather - roll your sleeping bag out in the sun during the day or hang it on the clothes line (whatever gets more sun) during the "heat" of the day, once warm, roll it up tight and leave it in the tent off the ground, when you go to bed unroll and the warmth from the sun will still be retained within for long enough for you to climb in and not feel the chill. even on a cold winter's days you should get a bit of sun...

