I think it's pretty (especially in an Irish accent) - and I would use the Irish spelling. People will get use to it and it's a lot easier than some.
Other names you might like that I think could go with Fearne:
Arwen, Ayla, April, Astrid, Asia, Asha, Aisling, Ailsa, Alayna, Aphra, Belle, Bronwen, Belen, Ciara, Cerys, Clara, Camilla, Cecilia, Cecily, Claudia, Catriona, Caoimhe, Diana, Elina, Eliza, Ember, Erin, Esther, Fabia, Faith, Gisela, Gabriela, Georgina, Harper, Helena, Iona, India, Imogen, Joanna, Juliette, Karina, Karenza, Lucinda, Lyra, Livia, Miranda, Melissa, Marta, Nicole, Nadia, Ophelia, Peronelle, Paloma, Ria, Serena, Saskia, Saffron, Shannon, Skylar, Thea, Tamsin, Violet, Vanessa, Willa, Zia.