For a good video on body rotation on the serve:
As far as using your legs serving, a big jump isn't necessary. Here is a vid of me serving - both my legs are pretty weak from injury.
If you can find a good video of Michael Stich's serve, it is pretty similar in the small knee bend. The back leg comes through with the hip rotation. An old-school style.
There's some McEnroe-ish serves just past 5:00. Maybe give that a try, at least for getting some practice getting some hip rotation. Lots of good video with his serve on youtube.