I am new here and this is my first post!

Hi, I got a Nissan Sentra N16 1.6XE 2001 auto, my gearbox is currently having a problem.
My car start jerking when I want to parking, I think the gearbox has reach its life, the mechanic says find one gearbox is cheaper rather than trying to fix it.
The question is:
1. I hope to improve my manual skills so I am planning to find a manual gearbox, is there any suitable gearbox that is nicely fit with my car?
2. If no, which auto gearbox is better or just find a ori gearbox for my car?

Thanks for solving my question!