Double knitting can be done with only one strand and one color, that's the only way I know how to do it. The way you describe working the rows - k1, sl 1 and repeat - is how it's done. You're basically knitting the sts that were slipped on the previous row and slipping the ones that were knit. Or it can be done in ribbing or other st patterns.
The tutorials in this blog
show several different ways to double knit including Single Yarn Double knitting, even though her samples show two colors, and she also explains how to work in seed stitch.