La Troupe black dress

I bought this dress from the la troupe online store. I wasn't happy with how it fit me because of how high the side slits are. Make sure you want to show a lot of leg if you purchase, I do not find my legs attractive enough to wear this....otherwise a beautiful dress. The reason it is priced as such because it has never been worn, only washed and this style has not been available in black. I just want to get close to what I paid for it. I am 5'7" 135 lbs and it fits just loose enough to still flatter. I can't remember if this is OS. otherwise, a S/M. Thanks!