Have you tried drafting it yet ? Have you drafted a pattern before ?
I would approach this just like a torso - take your measurements and just draw it out. I know that sounds overly simple, but if you've never drafted a pattern before I'd recommend you read up on it first and try something easier like drafting an upper-body block because that will get you to know the "basics" before you try something slightly more complicated like this.
Today I drafted a pattern for my friend who has a much different figure than I do and it was like doing something completely new - but you have to just do your "best guess" first try and just hold it up to them/yourself over and over again - taping on paper where you need to add more and such ! It helps if you have someone to help you hold it up.
If you don't think well that way or have never drafted a pattern before a "shortcut" way is to wear a pair of tight shorts (like bike shorts) you don't care about or cover that area with cling-wrap/et cetera and use duct tape to cover it. You have to be CAREFUL that whoever is putting on the duct tape is very gentle and doesn't compress anything or your pattern can turn out weird and pinching you in where you don't want it to.
This will also give you an idea of the comfort you can expect. You can add a bit of ease after you do it, too.
Are those stars on the fabric or are they put on on-top of the fabric ? I don't think it would be a bad idea to look for a satin with a small stretch content like 3% elastane/spandex/lycra - that will give you a significant amount of comfort with little visible difference in the fabric ! It looks like she's wearing a corset of some kind, will you be building that, too ? If so, I would wait to do the shorts pattern until AFTER you have that sorted out as you'd want to wear the corset and carefully cover and tape over it too so that you can account for the change over the top of the hips and the change it can make to the stomach's shape, too.
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan