Another Freeride Flow 30 cm would be good, as you aren't too heavy and you don't seem to be looking at larger sails for the Kombat 96.
If you are just going to be "back and forth" (slalom) sailing for the near term, you might want to look for a bit more vertical fin in the same size (28-32 cm ) range.
The Kombat won't be quite as "loose" with the more vertical fin, but you should be able to stay upwind significantly better, and should also be a bit faster.
Jibing with the more vertical planform fin will be nearly as good as with the stock 28 or 30 cm free ride fins, so there's really no downside to a bit more vertical for the use you suggest.
Not sure of the availability of True Amers fins in NZ, but here's the link:
Check out the True Ames Slalom Pointer, Sweep, and Convert for the shape/type fins I would suggest.
Hope this helps,