I support the previous warning about working with mains voltage, especially switching high current loads. Fire, shock and melted equipment are easily achieved. There are a lot aspects to mains wiring and switching including phase versus neutral versus ground, unintended inductance, contact arcing, heavier insulation, inductive versus resistive loads, spikes from relay coils, multiple phases, codes, etc. Hopefully, if you continue with the project and I'm not sure that you should, you'll be working only with single phase mains. I recommend switching both the phase and neutral, i.e. use a double pole relay. A common approach is to use a small relay with low current and voltage to switch mains or low voltage into the coil of a larger relay or contactor. Opto-isolation can be used to isolate the coil of the small relay from control circuitry if deemed advisable.
It's possible to setup a pair of small, cheap regular relays in a self-latching arrangement without the need to use latching relays per se. One of the small relays needs to be double pole (one pole for the latching circuit, the other to switch the coil of the large relay). Consider using flyback diodes on the coils of the small relays (assuming they have DC coils) and spark/surge suppression on the coil and contacts of large relay.
The reason electrons flow oppositely from the convention for current flow is historical. Early workers with electricity did not know what actually carried the charge through conductors, but they did distinguish between positive and negative. For uniformity, it was decided that current was to flow from positive to negative. Only later was it discovered that the carrier was the negatively charged electron, which moves from negative to positive.
Mike in California