I live in QLD... so it may not get as cold at night here, but only in the deepest part of winter did we have a bonds wondersuit under the 2.5tog growbag. I think our main reason was that she hates getting over heated, its a big fear of mine and she seemed fine. Right now in the temps we are having in Brissy if I were to dress her in something before she went to bed it might be a long sleave body suit with no legs under the grow bag. even lightweight flannelette pj's under the grow bag with the top few buttons undone. HTH!