m_c,

I would do it all with a 4066 quad analogue switch. Presuming the '12-24v line' is actually the logic input on the controller for the touch probe, which is resistor strapped high and the probe output is +5v when triggered.
You would use 1/4 of the 4066 to convert the probe output. 1/4 to switch the LED and you have 2 spare to use for other things, like inhibiting the spindle.

The 4066 has an 'on' resistance of about 80ohm (if my memory serves me).

Cheers,

Rob