How to reliably switch a DC analog signal that can vary from 10mV to 12V, and 1mA to 100mA
You can try to find the best relays, etc. But the proper engineering way to measure resistance accurately and also detect contactor faults is to use a 4-wire (aka Kelvin) resistance measurement.

Here's a diagram from this website:



You run your test current through one set of contacts and then measure the voltage through another set of contacts. By contacts I mean separate relays, switches, and separate wire connections.

Let's say your test current is set to 100 mA and can hit a high of say up to 10 Volts, and your DUT is 1 Ohm. So you would expect 100 mV across your DUT.

If your relay is bad and adds an extra 1 Ohm, your current source voltage will go up 0.1V to maintain the exact 100 mA you set it to, so that extra resistance will not affect how much current is running through your DUT.

Let's say a bad relay connecting the voltage sense also has 1 Ohm extra resistance, well the current through the voltage sense is 0 so that extra resistance is ignored also.

Let's say your relay is super bad and cannot flow current. Then your current source will try to push 100 mA through the DUT and it will hit its upper limit of 10 Volts. We can set our 4-wire meter to give a fault indication when it cannot supply the test current we have set it to.

So basically, with a 4-wire measurement circuit, you can:

1) Ignore resistance in test probes, cabling, and switch contacts.

2) Determine when there is a gross fault in the measurement system.

3) Obtain very accurate resistance readings of your DUT.

Keep in mind you don't need a separate current source and voltage meter; there are plenty of bench meters that do this 4-wire sense.

This webpage has a very thorough explanation of 4-wire measurements.
https://www.cirris.com/learning-center/general-testing/special-topics/40-4-wire-kelvin-testing