I'm sorry to hear your news.
I was in your position just over a year ago. My thoughts would be:
- think of your mare: even if she were sound, what might you prefer her to be able to do better, more ably?
- where are your ambitions, recreational and competitive?
- what are your timescales?
Basically, my mare went unsound two years ago and it was touch and go whether she would ever come right; but even before that I'd always wanted a horse I could happily take out to shows, clinics (English or Western) as she got quite stressed; I also wanted a slower

horse! And one which could introduce me to Western in the next year or so without threat of me breaking it

. So when put in your position, I had a reasonable template to compare against.
My advice would be: Don't rush into trying to breed a Western P-B unless you've got a very clear view of the attributes you want to bring forth; don't overlook your mare - the best of times, IMO, that I had with my mare was when she needed the greatest care; yes, I was lucky, she came good, but I'd wager that if I hadn't had that caring and looking time with her, I wouldn't be getting the 'give' out of her that is just so special now; and if you do wind up looking for a 2nd horse to continue your Western pursuits, I hope you find exactly what you're looking for, there is so much out there but before you go looking, nail what it is that you want to achieve first.
I hope it all works out for you, best of luck

.