Heaven my friend who sells them is actually having a discount today for Friday the 13th, 13% off if you wanted to buy one today online! She ships to NSW.

Let me know if you're interested.

As for how big - they need to be about 4 mths, starting to develop head control. Not sure if there is a weight range...

ETA - Ergobaby website says if you want to use the carrier for babies younger than 4mths then you need an insert. Doesn't say weight. I think it's because of their spinal development, or lack thereof, before 4mths.