Gift/Work/Social Etiquette

I'd like some advice on a tricky work/social situation.
A workmate is leaving in the next few weeks and I'd like to buy her a small present.
We get along really well (with a little bit of sexual tension but we don't go overboard with it),with the odd workmate thinking that we are seeing each other.
She is half my age and if i didn't work with her I'd be on her in a second (workplace romances are a no-go with me).
She has a steady boyfriend and I want to buy her a small gift but don't want to give her (or the boyfriend!) any mixed messages.
First question is, 1/ Should I buy her anything, and 2/ If so, what?.
A workmate is leaving in the next few weeks and I'd like to buy her a small present.
We get along really well (with a little bit of sexual tension but we don't go overboard with it),with the odd workmate thinking that we are seeing each other.
She is half my age and if i didn't work with her I'd be on her in a second (workplace romances are a no-go with me).
She has a steady boyfriend and I want to buy her a small gift but don't want to give her (or the boyfriend!) any mixed messages.
First question is, 1/ Should I buy her anything, and 2/ If so, what?.