For your size you'll want to browse around for a seller with thorough size specs. Aliexpress and eBay have many sellers selling forms and plates being produced in and sold from China and the prices for those are very competitive. I've no not tried a breastplate yet, but I understand quality varies a fair deal. If you want good service and, probably, the best quality, you'd check a dealer like The Beast Form Store, though their prices are some of the highest I've seen for plates.
I have purchased and worn some of the lower cost Chinese forms sold on eBay and found them entirely satisfactory. If you look around on YouTube you'll find a few video reviews of breastplates and similar products. From watching them I wouldn't consider the fuller coverage items with legs or arms covered. Those tend to wrinkle and look quite phony. In fact the high necks of some breastplates can look very unnatural as well. I think a first time user would do best to just buy one of the minimal coverage plates that are similar in coverage to a bra.