I'm in the same boat when it comes to gaming. Primarily use a trackball mouse and have used it for some games like World of Warcraft or Path of Exile but a traditional mouse is still king for any FPS game.

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.

Consider trying a vertical mouse. They look odd and the first day or two it is strange but after a while it becomes second nature. It was only after using one for a few mo ths that I realised most of my issues with typical mouses.

Also it is funny going back to a standard mice, it feels like you are awkwardly using a tiktak for input.

Some people use console controllers on pc playing competitive FPS games (see for example TheBrokenMachine), maybe thats an alternative for you? Personally I think it would take me 5+ years to get used to tho…