If you are looking at the Deluxe nightgowns, they run a little big. I bought size 4 for my daughter in the Rapunzel one and size 5/6 in some of the other princesses that were on clearance earlier. The only one she can wear is the size 4 because the 5/6 is so long it drags on the ground.
The Rapunzel one is not a scratchy material on the sleeves. The mesh sleeves are really quite soft. I like the deluxe nightgowns better than the dress up dresses that cost twice as much and are really rough and scratchy.