3.5mm, I now know why conventional consumer audio devices don't use mixers, they're a ground loop party

It's also that I don't know how to build a differential input not limited to power supply range, I do think they are sold and I have a mixer at home but it's somewhat bulky for my computer desks.

Got it. In my studio I have mostly unbalanced cables but the gear is all good quality so I never had any issues.

I think there are ICs for that specific purpose? If I understood your second paragraph correctly.