Last month Addition-Elle introduced their Smooth Curve bras. There is the option to have either a soft cup or underwire but both have the seamless back wings to eliminate back bulges.
They are available in sizes 36C to 46DDD and at the moment there are only two colors, black and mokamocha (looks like nude to me) selling for $49.99. You can have a look at it in motion on the incredibly gorgeous plus size model Ashley Graham:
Addition-Elle is a Canadian retailer that ships throughout Canada and the United States.
* Get your plus size back smoothing bra from Addition-Elle