If your heater resistance is really as low as 0.025R you will have trouble with a MOSFET as they usually have an on-resistance of about 0.1R. Therefore most of your heating energy will be going to heat up the MOSFET.
Find a better supplier of MOSFETs, 0.005 ohm is not too hard to find, 0.01 ohm is pretty commonplace these days (unless high voltage parts). They can be commoned up for higher currents, and frankly when we are talking 62.5mW its not a great problem.