leasha.
I had DD in a sleeping bag over summer night - not days (most nights) - she was 5-8 months at that stage and it was very hot (we lived whitsundays with no aircon - just the fan).

It was more of a comfort for her at night time as she had been in them since birth.

Anyhooo - i got a 'the dream bag' from the UK. i think they have sales atm . it is only 0.5tog which was the lightest i could find and it is gorgeous! Embroided and really long - she still fits in it... but we don thave her in sleeping bags this summer as we are transitioning to a big bed.