This free pattern from LBG Studio, which I found via Pretty Prudent, is pretty simple to put together... I struggled a bit with connecting the shoulder straps- they kept getting gummed up in my machines (both the sewing machine and the serger), but in the end they're serviceable, if a little bit lumpier than I would like. The topstitching also made the edges of the bodice a little bit wavy, even after pressing, but it's not the end of the world.
I upcycled fabric from the skirt of an Old Navy dress I found in my closet that I never wear and lined it with white knit from an old tank top. It's a size 2-3T, so I'm hoping Z can wear it as a top layer over leggings and a long sleeved shirt for this fall and then by itself next summer.