By not materialistic I mean someone who just doesn't have interest in material things for the sake of the value it would give them from their possession, but rather acquires them for their functionality or simply because they like it for them.

What do you call a person who is not materialistic?

Ascetic is defined by Dictionary.com as: a person who leads an austerely simple life, especially one who abstains from the normal pleasures of life or denies himself or herself material satisfaction.

What is the opposite of a materialistic person?

Opposite of being overly concerned with material possessions and wealth. spiritual. abstemious.