is it mayby an option to shape a SB gemini with twinzers? The board is wide enough...
you can use smaller fins and sail in shallow water... ( I am restricted in sailing on different spots because not all spots have enough draft for the gemini )
you can sail two big fins and get more low-end... ( And get even more fun with less wind, than you already have now! )
two big fins can produce to much pressure on your ankles... (But on the other side you are also sailing with two people, so than you even can share the force produced from the fin )