The minimum thickness / strength of the boards depends on the spacing of the platform beams below them:
|Board thickness||Axis distance between platform beams|
|25 mm (9.8 in)||≤ 55 cm (22 in)|
|30 mm (11.8 in)||≤ 65 cm (26 in)|
If you choose thinner boards, they will bounce and sag uncomfortably, which does not feel safe.