A "latching relay" is not necessarily a special type of relay. It can be a standard relay with an extra set of contacts that's used to "latch" the relay. Actual "latching relays" are partly mechanical devices and are much more expensive than standard ones.
Use a momentary switch for your remote "on" switch. It of course will be in series with your coil supply and the relay coil. Now simply wire the extra pair of NO contacts on the relay in parallel with the switch. When you push the remote button, these contacts close, and current continues to be supplied to the coil even after you stop pushing the button.
The remote "off" function is just as easy. You have another remote button, this one normally closed. This is wired in series with the latching relay contacts. When you push the remote "off" button, current through the "latching" contacts and hence the coil is interrupted, so the coil lets go, and the latching contacts are no longer closed.
This can obviously be extended to as many remote locations as you like, all with one extra set of relay contacts and a completely standard relay.
If you must use an NO switch for the "off" button, you can use a small relay at the pump location to convert this to NC. Your remote "off" button pulls in this relay, which disconnects the NC contacts on the relay, which are wired in series with the "latching" contacts on the primary relay.
Relays are fun!