Saoirse Ronan's favourite film growing up was Titanic (1997), so she was overjoyed to not only act in a film with Kate Winslet, but to also play her lover. Ronan said to Winslet when filming: "Who would have thought, when I was eight years old, that I'd be kissing Rose one day!"
Kate Winslet said in an interview with The Hollywood Reporter that she choreographed her sex scenes with her costar Saoirse Ronan for this film. "It's definitely not like eating a sandwich," Winslet said. "I just think Saoirse and I, we just felt really safe. Director Francis (Francis Lee) was naturally very nervous. And I just said to him, 'Listen, let us work it out.' And we did. 'We'll start here. We'll do this with the kissing, boobs, you go down there, then you do this, then you climb up here.' We marked out the beats of the scene so that we were anchored in something that just supported the narrative. I felt the proudest I've ever felt doing a love scene. And I felt by far the least self-conscious."
Kate Winslet felt incredibly proud of showing her complete self in the intimate scenes; an aspect of middle-age romances seldom depicted on screen. "I'm getting older. I'm not gonna cover that up. That shouldn't be a secret; that shouldn't be something that's hidden. I've never felt so proud of my marks and scars. My body's not the body it was when it was 25, and I'm very, very, very proud of that. It was very important not to eradicate any of those natural things that are changing about me." Winslet described it as the "most empowering experience in my whole life."
Wanting to ensure that Saoirse Ronan would be comfortable and safe, Kate Winslet insisted that the filming of the intimate scenes was moved to Ronan's 25th birthday, so that she would be happy and relaxed (and allowed them to drink some prosecco in advance to calm any nerves). She also made certain that only female crew members would be in the room during filming.
Lizzie Wiscombe, a volunteer at the Lyme Regis Museum, was asked to record her voice for Kate Winslet to base her Dorset dialect on. Winslet listened to the recording for three weeks, including when taking her children to school. When Winslet read out a scene to her, Wiscombe was in tears. "The emphasis that she put on the words, the way she was saying it, it really could have been Mary's voice."