Right, I've examined Gwynnie's dress in detail 
and it's two dresses. There's a gold satin shift, which is fairly close fitting, and a mint lace shift that's a little bit baggier. The lace itself is extraordinary, which is what I think makes the dress. Unless you happen to know a lace-maker, you'd be pushed to find any as panelled as hers is. It would be clever to cut up a lace shawl, or even a vintage curtain or tablecloth, to create a similar effect - but you'd have to dye it first, and I don't know how much time and/or devotion you have!
There are two more unusual things about it, from what I can see. The lining's stitched in at the hem - normally it'd hang from the neckline - and that's what gives the lace overlay its slightly puffy appearance. As the top layer's a bit looser, it creates little waves when she moves. The other thing's the unusual dropped shoulder seam. It's a very creative piece of work :)
I was thinking you might find a salwar kameez to suit what you want. A lot of them are slim A-lines, and you could chop a foot off the bottom which will remove the fullness they tend to have around the skirt. I've just had a quick google but, tbh, I don't know what would be too bright or blingy for you ... have a look, there's a choice of millions! (And you get a pair of leggings & a wrap thrown in.)
If you do have time, a good dressmaker would love the challenge! But, then, if you have time ... I think we'll be seeing a lot of hasty copies in the shops soon! I found about 40 good lace shifts just now, and every single one is sold out.