I have a very similar dress from coast from a couple of years ago. I tried the ultimo body on but it was no good for me. The only way to feel supported (I'm a 30ff) was to yank it up so that the g string was cutting me in half. I ended up with a normal bra and low back converter strap that did up round the front. I got a dressmaker to add a loop to the dress and looped it round the strap. It stayed in place pretty well. The front of the strap was lower than my control pants so that helped keep it down. I felt a bit like a trussed up chicken all night but it is such a beautiful dress.