You'd need to cut a curve into the dress you already have, that's what I meant. I also meant to shape the bottom, not the top of the sleeve. The top would probably be straight more or less.
You can certainly add a sleeve on as you'd discussed before, I was just recommending how to make a sleeve to get the result in the picture you posted. The way you're planning to add a sleeve will work, but it won't give you a sleeve like the other dress. The way I've seen that technique done, a bit of the top of the sleeve (tube gathered on each end) is stitched to the dress and the sleeve then sits on the arm, not the shoulder. I'm not sure it would stay on your shoulder without some shaping, but it might. I hope that's more helpful, best of luck.
Ahh ok, I see what you're saying.
I'll make up a couple of test sleeves and see what works out!