Deep mattresses and toppers
If the topper stays on, it belongs in the depth measurement.
Depth is the measurement most ready-made sheets get wrong. A topper that stays on is part of the mattress.
Measure from the top of the sleeping surface down the side to the base. Include the topper if it is not removed at night.
Deep mattresses, hydraulic frames and floor beds are ordinary work for the Hong Kong workroom. Type the centimetres.