With my previous employer I was fortunate enough to have the automatic raises for performance like Wayne mentioned above.
I was also promoted twice in the 6 years with the company into higher positions based solely on my performance. They promoted me because they knew I was the right person for that role. That's what you need to do. Prove to them that you're indispensable. Make them realise what they would miss should you fall ill or decide to resign. Maybe they think like already? See if you can find out.
Asking for a raise or promotion because you're finding it tough to live off your current earnings is commendable, not selfish.
Good luck with it
