Well.......I'm a 32G and I have a NL dress like that, as well as one or 2 others. Here's what I do:
1. Go braless. Depending on the cut and fabric, I can get away with it if I take gentle steps and don't bounce all over the place. It helps if the fabric is doubled in the bust. Also I'll often wear a shawl or denim jacket with a dress like this. Also it's usually nighttime so bralessness isn't so.....blatant.
2. Wear a strapless bra. I hate these. At my size they just prevent me from breathing. And they don't look natural. You might have better luck.
3. Wear a stick on bra. YMMV but I usually don't find them particularly effective on me as I usually end up with one of them where it doesn't belong, like in my armpit or the floor.
4. Wear a same-colored bra and live with the double strap look (don't love doing this).
ETA: If you can find one with a drapey neckline like a slight cowl that's usually more forgiving than one that's just a piece of flat material across the bust. If I get motivated later I'll model one for you.