Backless bra

[herecomesthsun]

I just ordered this then realised I would need a backless bra, I am 34G.

Would this be enough, do you think?

something which does not have a thong would be good. I am 5ft 9ish and long bodied, and would prefer not to have a wedgie all evening.

bit daunted by Ultimo sizing here

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.