Gyro aim is a must, and if you wanna be the best you can be, I would also suggest learning Flick Stick, which in addition to using gyro, remaps the right stick to immediately turn to the direction you tilt it in, allowing instant 180s (at the cost of no longer aiming vertically at all). Steam Input allows you to set this up for any game. You need to initially dial it in by adjusting how many pixels a 360 degree turn moves until you can do two 360s and be aiming in the same spot. You can do this by temporarily binding a button to do a 360 degree rotation and then finding something in the game to stare at. You can find videos of people doing this on Steam Deck.
As for the controller, I'd currently recommend the 8BitDo Pro 2 or Pro 3, but if you can wait, the new Steam Controller should be even better.
I did learn recently that Zowie released an ergonomic version of their mouse that I plan on checking out though. Unfortunately there's just not a ton of options out there for ergonomic gaming mice.
Also it is funny going back to a standard mice, it feels like you are awkwardly using a tiktak for input.