Flying High said..
Something around 9.6'-10' and 130lt would be a good benchmark to start with.
At your weight you could go a lot smaller but too big a drop is a lot of work and commitment.
Sunova boards would be good
I agree with Flying High. I'm around 78kg and went from a 10'6 Nalu GT to a Sunova Style 10x29 @ 130 litres.
i moved to the smaller board for the exact same reasons as you.
Strangely I find the smaller Sunova to be more stable than the Nalu. I think it's because it sits lower in the water, and doesn't bounce around as much.
Really glad I made the change. Would love to try a 10x29 Sunova Surf, or maybe even smaller. As a custom board maker, they can make you any size you like.
Definately worth demoing something smaller if you can.