Schimmel, I totally get your reluctance. FWIW, I have a 4 year old Morgan mare. I'm 30 and while I don't have any anxiety, I DO have an awareness that I don't bounce like I used to. And with two kids, a husband, a job, blah blah there's even more on the line. I had a collapsed lung this fall due to illness, so I'm trying to be careful, and have a friend hacking my mare right now.
My experience thus far with my mare.... she was unbroke when I got her, though had some driving training. I think we pushed her to canter too quickly and she started bucking pretty hard through the transition. For a horse that was bred to TROT, and prefers to trot, she doesn't have a natural canter like a WB that's bred for the hunter ring might. So we've scaled back and are working on her balance at the trot, baby lateral work, building muscle, strength, and really emphasizing forward and straight! I see a huge improvement in her canter on the line, but we are in no hurry to re-introduce it under saddle just yet.
A crowhop here and there is one thing, but a bronco-style buck is different. Ideally, you have a professional starting or riding the horse that knows how to avoid pressing or picking a fight, and doesn't let them ever *learn* to do it. KWIM? I know LOTS of babies who never did any bronco bucking, ever.
My mare has the BEST brain, is incredibly smart, sensible, and sane. In a year she is going to be rock solid under saddle. She's a great mover and has a super work ethic. I think Morgans are awesome options for adult ammies, they are a very well kept secret IMO!