[Zenst]

Good point, for some it is like being forced to buy a two right shoes to fit upon your feet. Let alone the aspect of mouse size and the analogy gets down to shoes only available for right feet and then sizes 6 and 11 only.

With that in mind - how hard would it be to make a mouse which had a gel top that would mould to your hand. Could have a gel that is perhaps viscus when an electric current passed thru it and solid when not - allowing you to setup the mouse to fit your hand. As for buttons, well, that has been one of the easier ones to fix and about the only area you can customise a mouse (switch left and right mouse buttons) which is your standard OS configurable.

Though I'm not aware of any material that is viscous when a current is applied and solid when not - the other way around you have https://en.m.wikipedia.org/wiki/Magnetorheological_fluid