I was lucky enough to take a costume class in college where one of our projects was to make a form fitted top to use as a base when altering, or simply making patterns. We used muslin and made a very form fitted, darted piece that was basted together. It consisted of a front, and a back piece. This form could then be unpicked and used to show things like arm size, placement of waist and bust line. If I remember correctly it had darts from waist to almost the nipple going straight up the front, and also from the side starting approximately from the base of the armhole. There were also rear darts from waist to shoulder blades on each side. The form should show your real waist, have seams running at exactly the top of your shoulder, mark the point where you can feel the bone stop at the top of your and have seams directly down the middle of your side. It should mark the top of your collar bone. You really need a partner to help fit it, especially to mark the back darts. This form does have seam allowances.

Tip on patterns without seam allowance. Get some kraft paper or butcher paper and copy the pattern then draw in seam allowances all the way around. You can trace a pattern on the paper in pencil, then use the above muslin pattern laid flat, with all the darts taken out, to make sure it will fit your body.