Do you know what's the hardest thing about writing a different genre? Of course you know. You've been struggling with it for a few months now.
Voice.
You want the new book to have your trademark touch--that special male POV--yet different because it's a different genre. Dilemma, dilemma.
Your trying First Person POV is making a difference. Stop second-guessing about first-or-third-first-or-third and keep writing. Because the moment you can stay in one character's head and move the story, you'll forget to worry about anything but the story.