Go for it, both of you - we're finding it so so helpful with Felicity. Already she can do about 30 signs, and we feel like we're communicating so much with her and appreciating what she's interested in (at the moment, clearly hats and bags. She can spot someone with hat or bag a mile off, and signs enthusiastically
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Sara, we're using the book "Baby Sign Language for Hearing Babies" by Robyn Warburton - it's based on NZSL. The website also has a e-learning pack that you can download with charts to print.
http://www.babysign.co.nz/ That's the only site I know of that's specifically NZ signs, but there are others that have BSL or ASL.
I also find the official NZSL site useful for words that aren't in the baby sign book - they have a good video dictionary of signs. if they're too tricky for little hands, I make up an easier variation. And we've completely made up some of our own signs too for more unusual things (eg mango
I found once we started I got into the habit of signing more quickly than I expected - and now F reminds me!