Switching a current with an NPN transistor and a P-MOSFET
You can just use the PMOS, and use a pin switched from output low to high impedance (e.g. input) to switch it on/off:



The 10k&Omega; resistor holds the FET off when the ON-OFF signal is left floating (i.e. your pin is an input/high impedance)
Then when the pin is driven low, the gate is pulled to ground and the FET turns on. You need to make sure the P-ch MOSFET you use has a suitably low Vgs(th) (turn on voltage threshold - some can be quite high) so you want a "logic level" MOSFET.  

Simulation: