Learn English – Difference between “Merchandise” and “Goods”

The term "good" in this sense is kind of a squishy term. A commodity is simply something that can be bought and sold. Futures contracts are commodities, as are financial instruments which may be abstract in the extreme. Often these are called products. The Gross Domestic Product includes goods and services. But goods are definitely distinct from services. Whoever said commodities are goods is probably restricting the definition to to material things, but that's a distinction of convenience, not an absolute definition.

In this context, I think if you're looking for a noun from the adjective extreme, extremity (singular) is your best bet - meaning "extreme-ness".

Ex: The extremity of his reaction

The words extremity (singular or plural) and extremes have a few separating points.

One is that extremities can refer to physical things (your hands and feet, the borderlands of of country), while extremes generally mark ranges (as in temperature, weight, etc.) and other more abstract concepts.

Another difference is that extremity, as noted above, can be used to mean "extreme-ness", whereas extremes doesn't convey that meaning. Thus, the extremity of his pain makes more sense than the extremes of his pain.

Extremity is also the word used when describing dire situations. It connotes a level of hardship that extremes doesn't. Thus, help in extremity means help in desperate situations. Help in extremes doesn't sound quite right.

Particularly with the popularization of "extreme sports" and "extreme lifestyles", extremes can sometimes have a positive connotation that extremity can't.

There are also places where either word can be used with equal impact. In a desperate situation, you might be driven to extremities or driven to extremes - both mean drastic action.