Yeah, I agree with Outraged . Your tastes are similar, you just haven't found an actual name to agree on yet.
I love Nyah, Iris and Ivy and like Piper, Cooper and Ivo (which I think sounds great with Theo)
How about:
Ayla, Aria, Asha, Alexa, April, Ariel, Annie, Ada, Aphra, Bronte, Brodie, Betsy, Cara, Ciara, Callie, Cassie, Dana, Darcey, Dolly, Emme, Effie, Erin, Enya, Etta, Elin, Eden, Fallon, Faye, Giselle, Heidi, Hebe, Halle, Iona, Isla, India, Ida, Josie, Juno, Kyra, Katy, Kyah, Livia, Layla, Lyla, Lyra, Lena, Lila, Lana, Lara, Lilia, Lois, Luna, Mila, Mina, Mala, Martha, Maisie, Maria, Mary, Nia, Nora, Nancy, Nina, Orla, Opal, Pippa, Polly, Posy, Quinn, Rosa, Robyn, Romy, Rowan, Rowena, Saffron, Sorrel, Sylvie, Silver, Sadie, Stella, Thea, Taryn, Tegan, Una, Verity, Vashti, Vada, Wren, Zia, Zara, Zillah
Arlo, Ashton, Artem, Aidan, Austin, Asher, Archer, Brogan, Corey, Callum, Dexter, Ellis, Elliot, Evan, Finn, Hunter, Harley, Heath, Ivan, Ivor, Joel, Jonty, Jesse, Kester, Logan, Lincoln, Lennox, Mason, Morgan, Milo, Micah, Nico, Owen, Parker, Preston, Quinn, Riley, Rory, Sonny, Solly, Tian, Talon, Vinnie, Zack