Speaking to Cinema Blend, Morgan said that the untitled rock biopic will centre on Mercury's troubled relationship with Queen bandmates Brian May, Roger Taylor and John Deacon.
Morgan said: "I didn't want to write an AIDS movie, to be honest with you. And then, I just looked at the period. It's sort of where he rejects [the other members of Queen] and comes back to them. It's sort of like a family movie. It's sort of like I hate my family, I want to be independent, and then I come back."
The Oscar-nominated writer admitted that May, Taylor and Deacon - all producers on the project - are offering advice, although he is not "sure how much they'll like what I write".
"I think they'll recognise the truth in it, but it's a series of painful memories for them," he explained. "I'm essentially writing about the most painful time in the band's history."
Cohen will play Mercury in the movie, which will reportedly end with a recreation of the band's performance at Wembley Stadium for Live Aid in 1985.