Wow, this was exactly my problem! Fortunately, I DID get advice from a more experienced "mature" horseperson, and now my mare and I get along fine. Also, i took advice from an executive at Google: What would you do if you had no fear? It changed my whole riding outlook.
If you need to build up confidence again, get a pony. It really helped me after I had a fall with my horse because the pony I rode was wild, but he was short so I wasn't afraid to fall.
Doesn't make sense to buy a 6 year old-- still a bit young would have bought something more 13 ish. And a pony is a good idea too. Lessons would be helpful.