I bought some last year from Target for DD. She was the same age. I looked in the baby section and there were some labled 00-000.. even though she was in a size 1 they were huge and fit her fine. They came in a 2 pack of white and baby pink.
When DD was smaller I found some Marquise brand bloomers in Myer which were plain cream/white with a couple of ruffles. Also you can try Ebay, lots of people make their own and sell them on there, I bought a beautiful pack of 3 bloomers on Ebay last Summer.
Bookmarks