A space mouse is a great help in Altium's 3D mode (especially because some of the 3D Body commands disable the regular mouse-based 3D view control for some stupid reason). It's also very useful in other 3D applications of course.
I'm surprised you want to *decrease* your use of the keyboard in Altium, the mnemonic/hierarchical keyboard shortcuts are one of the UI things they got really right IMO (well, except where there are inconsistencies between sch and pcb that I keep tripping over
). They're super fast when you get the hang of them.
Personally I use a Logitech M510 on all my computers, mainly because the forward/back buttons are essential, but for CAD productivity I switched to a keyboard without a number pad and put a separate number pad on the left side, so I can use it with my left hand while the right stays on the mouse. Being able to hit the numpad +/- keys for layer changes, or Tab then type in a number without taking my hand off the mouse is a significant ergonomic improvement. Using a keyboard without a number pad means that I can have space mouse, numpad, keyboard, and mouse all within a comfortable width.
This is the number pad I use:
https://www.amazon.com/KcBlue-Mechanical-Numeric-switches-Computer/dp/B08QZQ6L88/The backspace and tab keys are especially useful, and the mechanical keys are similar to the ones on my main keyboard which is nice. I have a little 3D printed thing that connects it to the main keyboard and props it up to a similar angle so it's almost like one device.