You can get new springs, we got ours from ARB. If you go for too much lift you might have problems with the control arms, our lift was 43mm and that caused no dramas at all.
You'll find these springs are a bit longer than standard but the wire diameter of the coils is larger. I have an ARB steel bullbar, 3mm steel bash plates, 9" Kings driving lights, 20" light bar and 3" DRL's all adding extra weight biased to the front springs. After all that, like Old Tony my D40 is 40mm to 45mm higher.