I would really appreciate your help in clarifying the possibility of immigration to Spain in my, rather specific case:

I'm a guy in early 30 and I have a non-eu citizenship (although my country is a candidate for EU - ex-Yugoslav). We do not need visas for EU/Schengen states up to 90 days within 6 months period. This is of course just for tourist visits, not for work, studying, etc.
I do have a job, but it is not connected to my permanent residence, as I work as a consultant on international mission for a big inter-governmental organization. I have a quite big annual income, above average for EU.
I live with my partner (we are not legally married), and she is an artist, without stable income.

We are currently checking the possibility of immigrating to Spain together, and most probably buying a house/flat. We do not intend to change our citizenships, but we hope to receive a residence/work permit. In this case, I would be paying taxes for my income in Spain, as in my case they are connected to the place of residence, not the citizenship. The work permit is more important for my partner than me, as she would like to start/continue her career in spain.

For our specific case, I am not able to find info online, and I hope you will be able to help us. Many thanks in advance!