I prefer the spelling
Una (though without any accents) because the 'oo' looks weird to me although it is quite cool. Definitely different in a good way - sort of eyecatching without resorting to M'KyLeeSyn or Shayellaleighanna :) (I hope these two are not actually in use).
I like the name and the spelling
Una is on my list.
Oona MargaretOona VerityOona SuzanneOona JacquelineOona DaisyOona WinifredOona GraceOona KirstinOona CarysOona MorganOona FrancescaOona HarrietOona MaeveOona ArianeOona MaryOona ThereseOona LeilaniOona ConstanceOona JoyceOona Madeline
Katherine Oona Rosalind OonaJennifer OonaMargaret OonaFelicity OonaSally Oona Annabel OonaMarigold OonaDanielle OonaLilias Oona
I think it works better as a FN. I found that as a MN it merges with the other name. The ones I've come up with don't seem to flow and I discarded many because it sounded like one name - Ruthoona, Lauroona, Nerysoona anyone? :)