I am knitting the Caramel Sweater by Petite Knit. You knit the ribbed turtle neck, then do german short rows for the neck edge, then do the yoke, then split for sleeves and body and continue knitting in stockinette until X inches “measured mid back from the transition between the neck edge and the yoke”.
The only issue is…I have no idea how to tell where the neck edge was finished and the yoke began? I also knit the sweater in black yarn, so harder to read the stitches 
The transition between the turtleneck edge and the yoke should also be the transition from ribbing to stockinette stitch. If you worked the turtleneck in rib then you should be able to see that change in stitch pattern. Once you see it you can mark it with a stitch marker or safety pin to make measuring easier.
The length of the sweater is also more or less your preference, depending on the amount of yarn you have.
I do like Petite Knits patterns including this classic.