Re: question about suit fitting
Obviously you're looking to buy off the rack. W
That bein said, you should absolutely be trying them on before you buy. Every manufacturer tends to be slightly different from the last, and even each manufacturer may be different for each style suit.
As for a back protector...yes, you want one. Whether as part of the suit (mine was custom made with one in it), or to be worn underneath. You'll want to make sure tere is enough room in the suit for it.
Remember, the suit is NOT supposed to "feel right" when you are standing up. They are cut for the riding position, not walking aroun in. When you put one on and it feels tight in the crotch, it's supposed to. Put it on and sit on a bike leaned over. That is where you will find if it fits right or not.