I found this Mccall's pattern
, which is a good template and includes bust darts. Just change the bottom hemline to a "vee", remove the right sleeve, and edit the front and back neckline. You may have to add a zipper/velcro
in the center back or side. Remember to include extra fabric for seam allowances. The two pattern pieces may end up being identical if you want to same neck line for both front and back. Otherwise the front pattern can differ slightly from the back.
Instead of cutting out whichever pattern you find, I would trace over it with tracing/pattern paper. This way you can reuse the same packaged pattern for something else. Also, if you're nervous, make a mock up with extra or cheap fabric. If it doesn't fit correctly you can edit it before making the real thing. I am not very advanced at sewing but hopefully this info helps!