I use a grip like Warne, I think that one makes you get a lot more spin because it makes it easier to get out the seam perfectly.  One of my mate uses a grip similar to what you are saying, although the index finger is more to the side and the middle finger on top and the ring finger and pinky the more conventional way.  He's by far a better bowler than me but doesn't spin it as far as I can. 

 

Your brain is your most powerful tool, just think about getting the ball out straight (as in not have the seam slanted and get the seam out not wobbling) along with strong revolution and it should turn no matter the surface.

 

Also, this is not something you hear being talked about much but as a leg spinner, it's important not to be too close to the stump.  Number 1, you might tend to drag the ball across and lose spin when trying to bowl outside off.  Number 2, release the ball in an inward part through the air gives it more chance of curving and even if not curving, it makes it much easier to get it to turn.  Go watch some Warne clips and you'll see something about most of his big rippers to right handers.  Path inward through the air, gets the ball to curve, drop and spin wickedly.

 

As an off spinner, the same applies, getting to close to the stumps mean your arm goes across you when you are bowling outside the off stump and the ball will mostly just slide across the batsman.  Bowling wider and with the inward path through the air makes it a lot easier to generate turn.

 

Lastly, its wise not to over think things through too much, you end up complicating yourself.  Take it from me.  Things will take time to work out.  If your grip feels fantastic, don't change it, that's a good start.

 

Also, when I get a big leg break, it always bounces WAY too high.I pitch it very full outside leg, batsmen misses and it goes quite far OVER middle.Any advice would be greatly appreciated.