Contrary to what I've read and expected, I've found hard rosin to work better than soft stuff. I use cello rosin actually. And also tight hair. Another counter-intuitive thing for my all-gut set, and it might just be my bass/particular string combo, but for some reason I've also found the lower wound strings easier to start closer to the bridge than the bare G&D, especially for lower notes and open strings. So you might try just a little closer to the fingerboard on your G&D? A little more bow pressure at the beginning of the note, slackening off immediately to sustain.