I'm 72 kg. TLDR - my big wave board is smaller (less litres) than the middle board.
A big board for lighter onshore conditions at home is a 85 litres thruster, 57.5 cm wide, with a bit wider tail area, but still performs super well for my weight when the conditions are not too powerful.
A normal board size for nearly all conditions, and also my travel board size is 86 litres quad, 57 cm wide, with fast bottom but with a bit thinner tail than the production boards usually have. Using very small area quad fins with it in all conditions, sails 4.5, 4.0, 3.5 mostly, rarely a 3.0 too.
And a small board is a 77 litres thruster, 55 cm wide, sails 4.0, 3.5, 3.0. Does not necessarily have to be too windy for this board to work, just that the wind direction and also the wave quality should provide enough power for going down the line if needed.