Looking for offshore snorkelling in Australia

We will be there for 4 weeks in January. We land in sydney and have time booked there. I am aware of Gordon's Bay to check out in Sydney area. I'd like any other suggestions for around Sydney. but also a beach destination that we could stay at that has offshore snorkelling. We are looking at Ningaloo Reef but it is quite far from Sydney and I am not sure if January is the best time there?

Any suggestions would be great!