ESP8266 reduce power consumption caused by extra ICs/components on board during deep sleep
Removing power from the sensors is the best way to reduce power consumption when you don't need them.
You can do a low-side switch because your sensors don't use a lot of current so that ground will be so close to real ground that it won't matter. The pins of the sensors however may be at VCC level so you have to watch where they connect, for example the I2C lines to your MCU, the inputs there have to be floating. On the other hand if you use the high-side switch then of course your I2C lines need to be low or otherwise the pull-up resistor on those will send power into your sensors (something to keep in mind if you are really trying to minimize power consumption).
When you talk about a mosfet and you say &quot;full-close&quot; that means it is &quot;ON&quot; because you have to think of it as a switch in a circuit, for example think of a knife switch. It's not a valve in a water line so that can be confusing, but to answer your question a pull-up on the p-channel is enough to keep it completely off (aka open) (not accounting for leakage, check datasheet when in doubt).