I use a single tube return into my keggle mash tun, and it has not needed any kind of float. My technique is just to use a long piece of thermoplastic tubing (it is stiffer than silicone or vinyl even when hot), making sure it is long enough to come into the MT, and then circle around the inside almost one full revolution. The stiffness of the tubing holds it steady against the wall of the MT, wherever I chose to put it. I submerge the end by about 1", and recirculate almost wide open.
It stays put against the side, and I can then use it to determine water level consistency during fly sparging.
Floats are just not necessary and don't allow the functionality I have now grown accustomed to.
You can kind of see the thermoplastic tubing in these pics, and the flow is visible atop the mash while the recirc tube is partially submerged but stable.