Would it be possible to make a ceramic "veneer" for a wood floating shelf? You could make a 75 cm x 12 cm slab for the top, a 75 cm x N slab (N = thickness of shelf + thickness of top slab) for the front lip and a 12 cm x N slab for the visible side and adhere them to the shelf. It would be lighter and you wouldn't have to worry about a hollow form warping in the kiln.
(I've only been working with clay for a few months so I may be overlooking some potential issues with this method. I'm sure the veterans will have more insight.)