From a spearfishing, rather than pure freediving perspective, I would say you need more weight or a thinner suit. I am quite a bit bigger than you, but I use about 8.5kg with a 5mm. On the very rare occasions I use a 7mm it is more like 12kg (but if I am in a 7mm I am not normally diving deep) I always use a 5mm suit if the temp is above about 9c
cheers
dave
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