The force of gravity for an object 100 miles above the Earth is only 5 percent less than it would be on the Earth's surface, so zero gravity can't be the reason that astronauts float when orbiting the Earth.
It is true that, when you are in a free fall, you feel as though you are weightless.
It is also true that in certain situations, if you move out far enough, you can extend the length of your free fall.
An object in orbit around the Earth is always falling toward the Earth. The reason it is in orbit is that for every foot it drops, the Earth's surface, due to its curvature, also drops a foot.
So, once an object is in orbit, it's in a never-ending free fall. And that free-falling object feels as though it's weightless.