I have bought
Disney Store Cinderella, Belle, Jasmine and Snow White dresses from eBay for my 4.5 year old and I always buy the age 5-6, even though she's average size. The Disney Store dresses are far better quality than Woolies/Asda etc but the
Disneyland ones are even better. You pay a high price for them though! I would try to get a Disneyland Paris dress from eBay, if I were you. If you search for Disneyland Paris in 'fancy dress', you should come up with quite a few. Failing that you could always go on the French eBay - there are hundreds of Disneyland originals on there!
Happy bidding!
Juliette