You haven’t specified the proximity of the item used as money to the attainment of your end. That is the key to classifying an item as a consumer good, producer good, or medium of exchange.
The condition that “without it, it would not be possible to attain my end” applies to all goods chosen by a person in his action. Without a car, I cannot attain my end of commuting to work. Without labor, steel, rubber, and so on a car cannot be produced and my end cannot be attained. Without money, I cannot buy a car and my end cannot be attained. Consumer goods, producer goods, and money all contribute to the attainment of an end and therefore, all of them have psychic value to a person, not just the consumer good.
The item used as money is a consumer good to a person when he attains his end directly in one action with the item. Let’s say gold coins are money, and I hold a particular gold coin for its sentimental or historical value. When I do this, the coin is not a medium of exchange to me. I have classified it as a consumer good because it gives me psychic value directly. Then let’s say I give the coin to my son who classifies it as money. As a medium of exchange, the gold coin cannot directly satisfy my son’s end. The only function of a medium of exchange is to facilitate trade. He must eventually spend it to acquire a consumer good that directly satisfies his end.
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