Hi Paul B,
There are a number of choices you could go with.
I depends a little on what type of weeds you need to have the fin shed, and how much weed there is overall.
The newer progressive rake weed fins work really well in light weed conditions with most types of weeds.
Examples of these new style "progressive rake" weed fins would be the True Ames Shallow Water Weed fins, and the Tangent Dynamics "Reaper" Weed fins.
The more swept back traditional (more than 45 deg. LE) weed fins will pretty much shed all weeds, but do't go upwind quite as well as the progressive rake fins.
Examples of this would be the True Ames Blade Weed, Gorge Fin Co. weed fins, and the
Lessacher Design Duo weed fins.
The Lessacher Design fins have the added "advantage"of being Asymmetrical which helps shake off weeds more quickly.
At your weight, I would suggest at least a 36 cm weed fin (they have a lot more area than normal vertical fins), but probably a weed fin in the 40-50 cm range would be better.
Hope this helps,