I have 29 gallon with no sump and want to add an ato. The surface of my water has no dead zones at all and I'm certain it will trigger the float switch constantly. Would using a small overflow box to put the float switch in work?
No. That is an adjustable weir for an all in one tank. It wont work like you are thinking. It needs a small return pump to keep the water flowing into it.
You need something like the duetto sumpless ATO.
Or just do what i did for my sumpless setup and hook up a peristaltic pump to a timer and measure how much volume you lose per day. Might need some adjustments as the weather changes but so far so good for me.
I think in most situations surface agitation small "waves" are not going to make a big difference. Just set the float to the lowest acceptable level and you should be fine. Here is a drawing:
It's fine if the "wave" crests go over the float, the float wont activate unless the "wave" trough drops below the acceptable level.