cute! I think the main questions you need to figure out is where each element ends on the body. So maybe the top ends at the natural waistline but the pants (without waistband because you won’t need a waistband if it’s a jumpsuit) end at the high hip. If this is the case, then you’ll have to adjust the patterns to get them to meet, either by extending the top or bringing up the top part of the pants. It depends on what kind of look you want. It doesn’t look like there are any darts in the pants so it might be easier to adjust those instead of the top. If they’re both already meeting at the same point on the body then you just saved yourself some work. 🙂 Then there’s the zipper. You will need a zipper that goes down the top and into the pants and they’ll need to be in the same area. If the dress has a zipper in the back and you’ll want to put it in the back of the pants as well. Once you make your adjustments to the necessary pattern pieces, make a muslin using a cheap fabric and baste your pieces together enough so you can test your experiment. You don’t have to do any finishing or interfacing, you just want to get an idea on how everything fits. (doing this type of thing means tons of experimenting so be prepared.) From the muslin you can see if you need to make any further pattern adjustments. Good luck and let me know how it turns out.