I recommend the upper body worn by several posters inn this thread. It's not just your back that can get injured. Smashed my shoulder at Whistler a few seasons back- ended that trip abruptly!
There are several brands available. I found that I really like Troy Lee Designs upper body armour. Light weight, very flexible, and soft feel padding. I wear the short sleeve version, but there is a long sleeve that protects elbows as well.
Go to Extreme Sports Equipment and Accessories | AllSportProtection.com
and read up/watch the vids. They have a good selection.
BTW, if you are mostly jibbing/park riding, that's when you need protection most IMO.
And yes, the looks from others when you take your jacket off is amusing!