I think Lowenna is perfect. Or just Lowen (as in Benjamin Button - I assume also a Cornish name).
I don't know how these names are spelled tbh but I 'know' (as in they are relatives of friends, not that I know them well enough to write their names) two women with names pronounced Ee-ona (Eona? Iona?) and Eye-rona (Irona?) which I think are lovely alternatives to Iona. One Scottish, one Irish, I think.
Also:
Anwen, Arwen, Ariadne, Aurora, Arla, Ayla, Alana, Allegra, Alayna, Aoife, Bronte, Briar, Carys, Cerys, Cora, Caoimhe, Delphi, Dulcie, Demelza, Danica, Devora, Effie, Everly, Emrys, Ember, Echo, Eden, Eirlys, Eilidh, Erica, Erin, Evana, Ffion, Fenella, Fleur, Fabia, Giselle, Hazel, India, Indira, Isha, Jonquil, June, Jacinta, Karensa, Keziah, Larissa, Leona, Leonie, Lorelai, Lavender, Lyric, Lois, Marissa, Morwenna, Morven, Meredith, Misty, Mirabelle, Mirren, Maeve, Niamh, Nova, Nyah, Orla, Ondine, Peronelle, Paloma, Rowena, Rosina, Romilly, Ramona, Remi, Romy, Robyn, Rhiannon, Seren, Sorrel, Sienna, Sorcha, Tamara, Talitha, Una, Yolanda, Zeryn