Write an essay on Materialism in the story, "The Rocking-Horse Winner" by D. H. Lawrence?
There are certainly many approaches that could be taken with that as a topic. Discussing the aspects that the mother is dissatisfied with any amount she receives is one such aspect. Instead of finding relief with her monthly windfall, she instead wants it all. Instead of taking care of the debts she already has, she buys new things.
You could also consider that her son is trying to buy his mother's love-but the price is too high. He has never received any gratitude or concern for his efforts and ruins his health trying to please her. His earnings bought him nothing but an early grave. Or look at the ways his mother thinks buying things will make her happy, yet her unhappiness only increases.