If you want to get really low, you can make a version of something we call a "high hat" in film production. For us it's the crown that a head mounts to bolted to a plank of plywood. Since the head for a still camera mounts so simply, you can simply bolt your head to a piece of plywood and you're done. If you drill holds in the center as well as a couple inches from a corner, you'll preserve the ability to be low while still being able to tilt sharply down without seeing the plank.
Here's a film camera on a high-hat: