Since the supply you want to switch is only 3.3V, and the MCU probably also runs on 3.3V, you could simply use a single MOSFET and control it directly by MCU pin. No further components required, no extra power wasted.
400mA is not a lot of current, even a small 0.1Ω RDS(on) MOSFET will only drop 40mV under full load. And there surely are better ones available if you want. However, you will need so-called "logic level MOSFET", one which can be switched by low gate voltage. Older FETs may require 5V or more gate voltage to reach their rated RDS(on).
NMOS vs PMOS:
If you disconnect ground with NMOS, outputs of some chips may go to 3.3V, possibly causing problems if there are loads directly connected to ground on those pins.
If you disconnect the supply, outputs of the chip will go to ground. Possible problems if there are loads on those pins connected to the positive supply (you could turn off such loads together with the chip, if they are on the same 3.3V rail).
N channel tend to be better, cheaper and more common.