From photos & videos it looks like you could put in slats in a range of thicknesses and then plane or sand down the edge near the footwell so it went smoothly into the fiberglass edge of the seat. Once the edge is smooth, the height of the rest doesn’t matter much. You could also ask someone at the yard to go measure the thickness for you. You’d have to explain that they’d need to open the cockpit locker to see the end grain edge of the teak and measure that – and get a separate measurement for the wooden plate, if they can. Two mm sounds quite thin for a “plate”. It sounds more like a scrim or veneer, just to hold the slats (glued) in place so they’ll maintain their spacing on what might be a curved surface of the fiberglass cockpit seats. Keeping the slats glued to the “plate” and the plate glued to the seat may be tricky. The “plate” may end up getting ripped apart. Simply glueing the slats (carefully) to the seat individually might work better, though you’d have to work out their shapes beforehand.