Use an arduino and the floats as just sensors that trigger events in the program. You can use what you have and a £2 arduino nano and if you feel like it, easily add additional floats and time limits as to how long the pump will run, etc.
Or you can add a second float and set it up so one float triggers the pump start and the second turns it off. There is a recent post with a suggested diagram for this (I'll see if I can find it in a mo), but this now has two floats, the failure of either causes a problem
Tim