You may want to take some university courses in how to will more effectively without
willing harder or longer. Seriously, parameters that affect the resonant frequency of
the floor/stand/boom/mic system include pole length, weight and stiffness; weights of mic
and cable; and height and stiffness of stand. Playing with one or more of those may shift
the resonant frequency enough that someone walking by at a normal pace won't set up a
resonance in the system. Or put a thin tight guy line from the mic to the stand some
distance from the boom so the tension will stabilize the boom and mic. The sprung
gym floor is a factor otherwise not present in most performance venues.
Tiny movements at base will inevitably produce larger movements at end of boom, and
because there is negligible damping in the boom arm there's not much you can do about it.
Placing the stand as close to the wall as possible to minimise floor movement is about all
you can do. And fit windshields if air movement causes noise.
-------------------- Technical Editor, Sound On Sound