Beautiful idea to use Colin as a middle name. You could also have Colleen as a middle name for a girl? So sorry for what you've been through.
How about:
Bronte, Bryony, Carys, Cerys, Cecily, Camilla, Connie, Darcey, Effie, Etta, Eden, Erica, Fallon, Farrah, Grace, Giselle, Hannah, Hebe, Imogen, Iris, India, Juliet, Josie, Katie, Lara, Lana, Lydia, Livia, Maia, Nina, Nadia, Natalie, Orla, Phoebe, Polly, Robyn, Rowan, Romilly, Sadie, Saskia, Taryn, Thea, Verity, Zara, Zia
Bruno, Cole, Caleb, Corey, Dylan, Dexter, Ethan, Euan, Fergus, Felix, Gareth, Harvey, Hayden, Ivan, Jared, Jacob, Kyle, Luca, Logan, Milo, Micah, Nico, Orson, Patrick, Ryan, Seth, Titus, Tian, Vincent, Zachary