I have a very similar use case and you may want to see if there is something of interest in they thread:
I use a physical slider switch and two load switch ICs to shut off the power. I needed to add the extra components because I wanted to use a surface mount switch and could not find a suitable one that could handle the current requirements of the system. When this switch is off, only a very small amount of current is needed for the load switches and to maintain the real time clock.
You can still control the enable pin to achieve ultra low power "enable" sleep. So, there are two different power controls - a physical switch which is good for transport and storage and the ability to control the Enable line using code in your sketch.
Hope this is helpful.
Chip