A 4013 dual D flipflop based latch is likely to be more complex than the toggle latch circuit by the time you've added debouncing for the button. If you dont debounce the button it will toggle the output a random number of times whenever you press it, and possibly also when you release it, so the button behavior is extremely unpredictable - it may fail to switch or may switch then revert when released.
I recommend simply building the toggle latch circuit (which is known to be reliable) with 4000 series buffered inverters, or NOR or NAND gates wired as inverters. Tie inputs of unused gates to ground, don't leave them floating.
However if you want more complex functionality i.e. using one button for on/off and also other control functions, or wakeup on any button, or adding timed power-off you'll end up needing a MCU with an extremely low power sleep mode, powered via a micropower LDO regulator, which removes the battery voltage constraint.