Upgrading drivetrain components Sram to Shimano then Acera to Alivio, advice welcome.

[BewlayBrother]

I have a Subway 2 (circa 2014/5) that I bought 2nd hand about 3 years ago and it's been fine for my very modest needs.
However a recent ride along a path where the council had cleared the overgrowing vegetation led to a nice green (supple) length of thin twig wrap itself around my rear cassette bringing me to an abrupt halt. I managed to free it but the rest of the ride was unpleasant and I think it damaged the (Sram X5) rear derailleur.
I've checked the RD and it all looks true but it runs rough and replacement looks likely.
This has prompted me to look at replacing the shifters (Sram X3) as the thumb levers have long travel which is becoming increasingly hard to operate with the arthritis in the thumb joints.
I have another bike that have Shimano shifters and they are much better for me to use so I'm thinking of moving to a full Shimano set and trying to decide between Acera and Alivio however the Alivio only seems to do 9 speed on the rear (my current set up is 3x8) so would need a new cassette.
The Alivio is more expensive but not restrictively so if the return is worth it for a smoother experience.
Thoughts?

 

[Ajax Bay]

If you want to change what you propose should work. The 9sp cassette will fit (without any spacer required) on your wheel's freehub. You'll be wanting a new (9sp) chain to go with the new cassette. Combined that's be less than £32.
I doubt you'd notice any difference in shifting performance between 8sp Acera and 9sp Alivio shifters so for your 'modest needs' I'd KISS: stick on 8sp.

 

[BewlayBrother]

Thanks for the reply.
I'll do as you say and stick with the 8sp my thoughts to go to the Alivio were based on being able to get the right shift for only a fiver but by the time I add a new cassette etc it becomes a false economy.