CrossRoads, thank you for the response. It looks like this part could work. I don't completely understand what to do with the SHDN pin, however. I want to have a toggle switch that will cut all power from my battery, so that this regulator will be turned off when the switch is turned off. Then, when I turn the switch on, whatever voltage my batteries are at will go through this regulator and then power the Arduino Pro Mini. I don't think I need to use the SHDN pin for anything, but do I need to connect it to something so as to not leave it floating? I feel like if it's just floating, then it might want to power down?
Thanks.