Couple things about my plastic plate false bottom.
1. I don't spend a lot of time stirring, that's probably what causes them to float. A little stirring at mash in (not too far down, don't wanna hit the false bottom). And then a little more at mash out. I pretty much let the cooler do its job of keeping the heat stable, and it works.
2. I didn't drill a "bazillion" holes, and I didn't make them 1/8 inch either. The commercial stainless steel ones could pass 100 gallons per minute, and I don't know anyone that is gonna sparge that quickly. Slow down, this should take 1/2 hour to an hour depending on your batch.
I made my false bottom, when I was just starting out, and I was poor, I couldn't afford the Phils Phalse bottom that was available at the brew shop, and I don't seem to have the problems that others talk about with the false bottoms.
I found a 12" bucket lid at Lowes, and I am pretty excited to get my 10Gal round cooler, and play making some bigger beers.