Reflotron wrote: ↑It has 5 buttons though, so it does not really fit the "plainness" required.
The thing is I am using a lot of different systems and I just can't manage to configure correct button behavior for each of them. The main problem is accidentally hitting an additional button with some weird function the OS chose to assign to it (somehow segfaulted a linux system once that way).
5 buttons (primary, secondary, middle/wheel click, two side buttons) and scrolling in 2-4 directions are completely standard and generally work the same under every modern system.
If you want the exact same behavior everywhere, the obvious problem is middle/wheel click used for pasting selection in X.Org versus autoscroll in MS Windows and some toolkits.
Behavior of the pair of extra buttons is more consistent across platforms: it's back/forward everywhere (worst case: it's not recognized at all).
Every other button is (a) unknown to the host system (e.g., changes settings directly in the mouse), (b) unconfigured on any system (standard mouse buttons 10-12 either aren't recognized by the OS, or have to be explicitly configured by hand), or (c) a standard virtual keyboard key, in which case it can usually be disabled or configured with settings stored in the mouse (but you might want to avoid mice/trackpads "designed for MS Windows 7/8/10", because they have hardcoded keyboard shortcuts set to certain gestures, capacitive buttons etc.).