Here’s a free pattern in pdf format to print.
This one can be a bodice to add a skirt to, or lengthen the lines to make a flattering princess seams dress. I appreciate a pattern that doesn’t involve shoulder seams. Every fiddly step eliminated makes it that much easier.
It has a simple, modest neckline and short sleeves.
This is for the 1999 Bellybutton Barbie mold or “Barbie’s shapely new curves” as the commercial pattern companies call it.

Stitch neck facing to bodice, right sides together. At this point you can determine a more round or V-shape neckline, or larger neckline or more modest neckline, by the stitching line. If you want a really low neckline you might need to cut the facing larger or longer than the facing pattern piece I provided. Clip, turn, press and top stitch the neckline
Turn up sleeve edges, press and topstitch. Then pin sleeves into armholes and stitch. I found that hand stitching works best for that part. The sleeve fits into the opening without gathering, and it’s easier to just sew it by hand than try to pin two contrary curves together.
Sew front and back darts. It’s a good idea to mark the top of the dart and start sewing at the top to make sure both darts are even, because a slight variation is so obvious.

This picture is after sewing the front darts, I’ll do the back darts next.

Then sew up the side seams and underarm seams all at once.

The skirt is up to you. Decide how much fabric to gather based on how thick it is, and style the Barbie gown of your little princess’ dreams.
Try the bodice and skirt together before sewing everything up– if you use a gathered skirt with a lot of bulk, you might have to make the back darts a bit less to allow extra room.
And then the back snaps or velcro and it’s done!

Or use the extensions to make a princess lines dress. The skirt is limited to knee-length but you can always add a ruffle.