I will also recommend the Little Dress-up Shop! The dresses are branded "Little Adventures" and are sold other places (brand itself, Target online,
Amazon, etc.); however the customer service at LDS is second to none! Free, fast shipping, package deals, discounts, reward programs, and just stellar communication are all provided by LDS. I was really amazed.
As someone who spent years at TDS, selling princess dresses, and also has a degree in costume design and construction, these dresses are amazing! They are so incredibly comfortable (not scratchy, inside or out) and well-made, and reasonably priced ($25-$40, usually). Plus, NO LOOSE GLITTER, and you won't miss it. The dresses sparkle if they should due to unique trim and finishing selections. Unique dresses are available here, not just the ball gowns for each princess--they even have Aurora in blue! My daughter has been wearing her new Cinderella rag dress all week. We have 7 of these dresses, and expect more in the future.
We also found them through Moana--this dress is the very best Moana dress. I'm a bit of a stickler for accuracy in look, overall, due to my costuming background, but this one is comfortable. My 3-year-old was not going to wear a tube top, plastic straps or not. Why?! She just turned 4 and has never questioned the one-piece dress. She LOVES to play in it though.
That said,
Disney Store (TDS) changes their dresses out twice a year, spring and fall. Spring being an inspired look, and fall being more true to the film. The very first dress released after the film, will be the most film-accurate. The dresses are well-made, beautiful, and truly lovely, but chronically uncomfortable--especially in the heat. I recommend getting a nice, old-fashioned slip to wear under these to avoid seam irritation. These dresses will typically run $50-$200. The higher number being for limited edition ensembles. The dresses do have occasional sales and will clearance out, if stock is available, but don't count on it!
I believe the park dresses are changed out once a year, and are truer-to-film than some of the TDS spring looks. All of the above TDS info regarding quality/comfort applies. These dresses typically run about $70. BBB is now offering the signature collection, at I believe $350 a dress. They are gorgeous, but I can't even imagine as that was almost half the price of my wedding gown!
All dresses are washable, cold/gentle...or of course hand wash. Always hang to dry. The Disney parks/store gowns will take significantly longer to dry. Stain removers can be used safely. You also may consider the use of a large lingerie bag to help protect them. Hope this helps!