Un or Una Tesoro

Hi Guys,

hoping someone can help do I use un or una with Tesoro. I wanted to use the feminine version.

To explain what I need this for- I am trying to think of a name for a new ladies jewellery range in work. I wanted to something that rolls off the tongue and doesnt sound silly when not pronounced correctly as it will be in Irish shops so the chances of everyone pronouncing correctly is unlikely.

Would appreciate any ideas or just some help with the un or una question.

Thanks a mill