With two broken vertebrae, you might want to try getting into and out of a cobra before purchasing one. Not sure how much your range of motion is limited. They are not the easiest thing to get into and out of. You do not need to be a gymnast, but they do sit low and are a little cramped inside.
As I was reading your post regarding you being an adrenaline junkie, it made me thin that you are a prime candidate for vintage racing. After a race I am on an adrenaline high for about three days. However, before you considered going that route I would download the medical form for a vintage racing organization, such as SVRA, and take it to your physician to see if they would sign off on it given the two fractured vertebrae.
Good luck in your quest.