You definitely have a type! The Sa in Sadie & Samuel plus the -ie -y same sound at the end of Sadie & Lucy makes Sadie the perfect combination of your 2 kids names! I love it but for that reason think maybe some fresh sounds will feel more original for potential baby #3 (I won’t tell 
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My suggestions:
Alice, Bella, Daisy, Juliet, Phoebe, Willow
Alice is my favorite for you because Samuel, Lucy, & Alice all have the L and S sounds just arranged in different ways with different beginning and ending sounds. They’re all classic beauties 