I have the Vanson in my Vanson and Dainese HPC in my Dainese. The Dainese is precurved in and does not bend/flex enough outward to be comfortable......others have worn it though and find it very comfortable......The Vanson is comfortable but wish it was longer to go down the spine more.
Knowing what I know now I would opt for the kind Moto posted.
I have the Dainese back space protector - no complaints, tho I haven't crash-tested it yet (KNOCK ON WOOD!) ;D
As for suits, I recommend motorace.com, which is where I got my suit. Because they are phasing out carrying Dainese suits, they're prices on Dainese suits are great (to clear 'em out, I guess), but the downside is that they don't have every size. Worth a try, tho!!
I remember about 15 years ago my uncle was racing motorcycles in Holland. He was the only one to wear a back protector. Now they're commonplace and people wear them on their commutes. Cool.
Anyway, I like the Helimot TLV, to be seen at helimot.com Pricey but flat, comfortable, large (huge, actually) and very protective. I've had hard-shell protectors like the Alpinestars or Uvex (a German brand) before, and they really eat up your leathers should you find yourself in a decent slide on your back.