Mosfet gate voltage gradually open with the increase of gate voltage. You can check it proactically when Mosfet start conducting while increasing gate voltage.
For low voltage scenario, you can use npn transistor. Please search yourself to get approperiate npn transistor for your application
If your LED power requirement is very low, then you can use a transistor itself directly. Thing to remember is : transistor is a current driven device. Larger the output current (here LED current) larger the input driving current, which the processor may not be able to deliver.
Generally MOSFETs have a threshold voltage around 4V. Since your processor is working at 3.3V, you have to use a low power transistor in between the processor and mosfet.
Optocoupler is another option which will give you perfect isolation.