[Question] Evidence on correlation between making less than parents and welfare/​happiness?

Edit: Big thanks to all those who have responded to this. I have updated my views to be far less confident in my previous assumptions :)

I am in a friendly debate with a friend about the importance of finding a job that pays a lot of money. I am pretty convinced by the evidence that after a certain income additional increases barely increase happiness. My friend is skeptical about how these various studies assign causality and in particular thinks that they don’t pay enough attention to mobility. He claims that making less than his parents would be detrimental to his welfare and happiness since he is accustomed to that life style. My intuition says that he would just habituate to a less expensive lifestyle but he doesn’t think this is true. Does anyone know if there has been research on this? He has expressed that he would love to be convinced that he didn’t need a high paying job to be happy. :)