You might also get some tips by watching videos of people who knit continental style. People hold and manipulate the yarn differently even while using the same style, and one of their tricks might help you with tension.
For example, the woman in this video for German short rows (http://www.youtube.com/watch?v=P6n561SMZXQ
) uses her right index finger to hold the yarn on the needle to form the purl stitch.
I'm trying to adjust my purling to doing it this way because it looks like less finger fatigue than what I'm doing. And in the process of trying this out, I noticed that my purl stitches were tighter than normal--which means my tension was tighter.