Our September born DS was swaddled for the most part over the spring and summer, and we found that to be the most versatile and best value way of adjusting the warmth - we were given lots of wraps and blankets. When they're little and can't move much, I reckon it's ok the use a blanket tucked in over a well-swaddled bub (feet at the foot of the bed, still, as per SIDS guidelines.) Once he started to wriggle more, and we wrapped him arms out, that was when the sleeping bags came into their own. We have 2 very light ones (probably 0.5) and 2 2.5togs, in the 6-18 month age range that is available in the Plum brand (available at BabiesRUs.)

We find on the colder nights in Perth, it can get down to 11 degrees in his room, and below 16 deg he wears a singlet, wondersuit, and the sleeveless sleeping bag, plus a warm winter hooded jacket over the bag to cover his arms and head. He's warm enough with that, but I wouldn't want it to get any colder. Above 16deg, he's ok without the jacket. (SIDS guidelines say not to cover their heads, but I think they're expecting babies rooms to be heated, which our bedrooms are not!)

I definitely find the room thermometer on our monitor a really useful tool for gauging what he needs to be comfortable.