I have a Musical Fidelity NuVista Vinyl which can take up to five inputs, each configured either as MM or MC, with lots of loading options for resistance and capacitance, and remembers all the settings during power off.
The funny thing is that I ended up going back to my previous phono stage, using it set to MM, so I could use an SUT I had lying around. I use good quality switch boxes to select the three MC/one low output MI to go into the SUT, and then to select the SUT output or a pair of high output MIs to go into the phono stage. All interconnects are very short (1ft) and while it sounds like a nightmare of unnecessary connections, it works very well.
You don’t need a mono switch for a mono cartridge - the cartridge has taken care of that for you! So you could simply use a switch box if you just want to use two stereo and one mono cartridge. Something like this.