I find it's way easier to have something to rest the thumb on, so floating should be your last option if you're not interested in being even cooler than you already are.
Resting on strings is good too, but for the E string it's also good to have a rest for that string, which can obviously be a problem if you don't have one. Unless you're trying to preserve the authenticity of your bass I don't see why you would be opposed to installing a thumb rest... but if you are, you can play a little further down the neck and use the actual neck as a thumb rest. If it's not your comfortable distance, then you should consider making it your comfortable distance or floating.
It should also be noted that pressing your thumb into a stationary position against the face of your bass where you'd have a thumb rest is also an option.