How do I determine the pitch/roll stability of a buoy?

I am designing a loosely-moored spar buoy (large height relative to width), and the equipment on top needs to remain as vertical as possible while floating in the sea, within limitations of buoy cost, size and weight. I have done fundamental buoyancy and stability calculations that demonstrate that the metacentre (M) of the buoy is located above the centre of gravity (G) meaning the buoy is stable.

Stability increases as the metacentric height increases. But how do I know what metacentric height range to aim for?

Is there a more appropriate measure of stability (stability metric) than the metacentric height?

Or do I need to use complex calculations to determine the pitch/roll of the buoy for a given wave height and speed?