3.3V step up to 5V using BJT
The current in my coil is about 20A with 16V. The speed is not really
  important, it's only to choose which coil I want to measure. Any power
  supply.


Try this type of BJT interface to your MOSFET: -



The "switch" is just your 3.3 volt logic level input - feed it into Rb (maybe 470 ohms). Rc should be a couple of kohm and V2 should ideally be no less than 9 volts but it's likely the 16 volt that feeds your coil is fine. Make sure your coil (the load) has a reverse protection diode else your MOSFET will quickly die. If you think that the 16 volt rail may get a little higher, consider putting a zener diode across the BJT to protect the MOSFET gate from over-voltage.