I use the floor LOL ... And I've done it with queen sized quilts. I tape the backing to the floor, put the batting on it, then the top. Get it all nice and flat and then I spray baste it. Let it dry (I give it about 10 minutes, and then I flip it over, and can spray the backing to the batting and not have to worry about the front.
A bit hard on the knees, but it does work! You could always use knee pads!