I think if someone would go so far as to get body-altering surgery and hormone therapy, or even to simply present as a gender different to the love they were born with, despite the social stigma and bigotry they may have to face, it's impossible to say they are doing it for attention. Trans people are more likely to be killed or commit Self Delete, more likely to be shunned by their friends and family.
Don't even get me started in this mental disorder crap. Entertaining that notion, how do you propose it be dealt with? Don't you think the nutjob Christians who shove their kids into conversion therapy would have found some effective treatment? Yet they haven't. So even pretending it's a mental illness (you'd find the APA disagrees) it'd be better to alleviate the symptoms than use ineffective "treatment"