TonyWilk:
across-the-relay-coil won't work with a single-coil latching relay, but you can add several diodes like this:
The 4 diodes clamp the spikes from the coil switching
(ignore the LS244 part, I just googled for a sort-of suitable diagram from here )
Nice. When the coil voltage is exceeds around two-times the diode forward voltage, then this allows current through the inductor to flow, right?