Hi there, all the words are used correctly. Consumerist is an adjective, consumer is a person who consumes, and consumerism is the general noun to express the idea of consuming. 'Consumer society' is a compound noun.
Maybe some of the sentences could be phrased a little bit differently, this is how I would say them:
'What I don´t like about Christmas is the consumerism, a period in which people are becoming more and more consumerist every year. We are living in a consumer society full of consumers. I think this consumerism should change because this is not the important spirit of Christmas.'
So the second sentence says pretty much the same as the first sentence, so maybe you could reword the sentences and put them together. The only other thing is that Xmas is very informal, so I would stick with using the word Christmas if it is an essay or something like that.
I hope this helps!