Control a MOSFET using tactile switch with single power source connecting to gate and drain
The main feature of the MOSFET is very high Gate impedance, which basically means the gate-channel "connection" works like a capacitor. The only time when any significant current flows in the Gate circuit is when the Gate is loading its charge when its connected(happens very fast).  You could basically connect the switch between the battery positive terminal and the Gate, (and the positive terminal to drain and 0 to source) and it Will work without burning your switch, but a single resistor in series will limit the initial loading current. This way the current Will flow from drain to source when the battery voltage is over the threshold. Just remember to use some load and not connect the battery directly to the drain and source with the switch closed.