The Duro-Med Posture Corrector gets mixed reviews. Its main problem is that the straps can become uncomfortable and irritate your skin. To be fair, most products of this type are more comfortable with a light undergarment of some sort.
The product comes in a range of sizes:
X-Large XL (46″-48″)
One of the handy features is that it is machine washable (but be aware that a lot of washing will clog up the Velcro fasteners).
It is constructed with reinforced foam criss-cross bands for back support. This design helps correct posture and may reduce back strain. Available in white, 80% cotton and 20% Lycra, and latex free. Asking price is around is around $18 usd.