Studies are showing that more letal injuries occur as a result of blunt force trauma to the chest than originally thought. I would be looking at a chest and back protector combined.
Bohn has some REALLY good stuff and offer discounts for combination chest and back protectors:
http://www.bohnarmor.com/catalog/pro...=KC40%2FKC40CP
Knox has some really good protectors as well.
I wear a Dianese BAP1 protector. I like it but I have a short torso, so I'm always having to pull it back down or it's crowding my neck.
I HIGHLY recommend a back protector any time you are going to be doing "spirited" riding, and one with a chest protector is even better. Rolling back first into a sign post or rock outcropping could leave you rolling four wheels permanently instead of walking.
Most protectors are plated with the plates bending in only one direction. Upon impact the force will tend to bend the plates backward. When this happens, they plates interlock and become rigid.
They aren't that expensive, and you may never be in a crash where your back is exposed to impact, but it only takes one instance for your life to be irreparable altered.
Catheters and colostomy bags suck.