What about a wrap style sling like a Tyion Sling? They are one size fits all with no rings to adjust, just fabric to wrap to your exact size?

If it's of any consolation, I don't like my Ergo which I'm bummed about since everyone raves about them. It's too big for me, I'm small too and I can't get it to fit right. I loved my Tyion sling though, have lent it to my neighbour who has just had a baby otherwise I would offer for you to come over & try it, seeing as you're in Perth too.