I bought a 2XL 10-12 and the bottoms fit fine but the top was TINY, it barely covered half a boob. For reference, I had a baby 8 weeks ago, Im 54, ~160lbs and am nursing. I was a 6-8 or a medium before this pregnancy and have been an 8-10 or a large since my baby was born. I think Im like a 36G these days.
Also, the bottoms aren't lined in the back and are sort of see through.