How high do you need to pump the water from your refugium to your display tank?
If it's reasonably expected height (4' or less), an Eheim 1260 is going to be quite large. I use a 1260 as the return pump on our 90g reef and sometimes think it is too large for that even.
You shouldn't need any float sensors to prevent flooding. As long as your return pump is not pushing more water to the display tank than the drain can move back down to your refugium AND you leave enough empty volume in your refugium to allow for the water that will continue to drain from the 20H during a power outage (or whenever the return pump is turned off), you will not flood the floor.
What size is the drain on the 20H?