I finally settled on this one- https://www.ravelry.com/patterns/library/oh-baby-cardi- it is turning out so nice, but I am frustrated with the fit. I am using 4 mm needle (the instructions indicate to use 4.5- but I really don’t think that .5 should make a huge difference). I am following the instructions for six month size, and it looks like it would fit a doll- I think if I were to make it again, I would use worsted and at least a 5.5 for the six month size.
The Ravelry details page for the pattern says DK but the stitch gauge given is for a worsted on the 4.5mm (US7) needles. If you’re using a DK yarn and the smaller needles that could well contribute to the smaller size. You might measure your gauge on the stockinette portion of the sweater just to check that you’re getting 19sts/4 inches.
Your plan to go to a worsted at about 19-20sts/4 inches is a good one. Then you can figure out the needle size from there.