I've been talking to my friend Maggie about sewing recently. We're trying to apply what we've learned about fitting knitwear to woven garments. She's the one actually sewing - I'm just pondering at this point mostly because I can't find decent fabric. Unless you want to quilt or a wedding gown, fabric stores cannot help you. I want to make a sundress out of a lightweight cotton, but I am increasingly convinced that it will be Christmas before I find appropriate material - and even then, the fabric will be printed with candy canes and holly!
Anyway, I came across the following fabulous picture on Pinterest that shows exactly how to upsize a bodice pattern piece. Cut right-angle slices into the bottom right of the piece up to the armhole and then spread out the slices and tape the tissue. This makes so much sense to me. Look at how the shape mirrors a larger body.
I suspect you'd need to make a couple of other changes to get a better fit. I'd need to make the bodice longer because I'm busty; I'd just add another inch or three to the bottom of the pattern. The dart would also have to be lengthened a bit to have the point end at the right position on the bust.
But what a great way to approach this kind of mod. In the past, I've added inches onto the side and always ended up with an A-line tent regardless of the shape of the original garment. This method adds inches exactly where you need them and we know from experience that that's exactly what is needed to make a garment fit well.