Alivio, Deore, and XT will be absolutely fantastic quality and I doubt you would find any of it is 'worse' than what your bike came with.

You could do 3x9 or 2x9 both easily and without a lot or cost(relatively speaking) if you use Alivio and Deore components thru ebay and are OK with waiting a few weeks for deliveries from China/Taiwan.

If there is nothing wrong with your current derailleurs, you could keep them if you switch to a 9sp setup. So old derailleurs and new shifting/crank.