Hi vncoffman,
There isn’t a specific cut off weight where you would suddenly need higher quality materials and it will depend on how much over 200 lbs you are, your weight distribution and body type, your sleeping positions, the type and thickness of the comfort layers, and many other variables as well but the lower 200 lb weight range or higher is where I would generally begin to seriously consider higher quality comfort and support materials in the layers of a mattress that are most subject to regular compression and the softening and breakdown that goes with it.
There are some foam quality guidelines in post #4 here and there is also much more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here and the posts it links to.
Phoenix