I don't want one with holes in that will let it water. I also want it to look evil. Ha.
I was thinking of a motorbike helmet?
Probably a cheapo one to see how it works out.
Visor would be good.
Another factor is the road traffic noise. It's so loud these days. I think something covering ears might make the ride in a bit nicer..
Motor cycle helmets are far heavier than bicycle ones - unsurprising - and I think you will soon get sick of wearing one in a situation where you are doing physical work.
On another issue, whether you have to be going fast to kill yourself in a fall, you certainly don't have to be going fast, and it is nonsense to say that you do. Every year, people die from falling backwards onto the back of their heads. It is VERY common. Most 'one punch' killings happen not because of the force of the punch, but because of the fall onto the back of the head. People even die in ski lift queues slipping suddenly backwards on ice. Liam Neeson's wife, Miranda Richardson, for example, died in a simple 'toppling over' skiing accident, banging her head on hard packed snow. A friend and colleague of my partner, a doctor, suffered months of quite serious cognitive impairment after he fell from his bike at a very moderate speed, when a car clipped his handlebar and he struck his head on the road.
Nobody thinks wearing a polystyrene hat will save a cyclists life in every kind of accident. A lot of dead cyclists are actually run over and crushed by trucks and buses. What can be avoided is the potentially high number of deaths, injuries, and disabilities from head injury caused by tumbling from a bike in an uncontrolled manner. You don't have to break the skull to suffer a serious brain injury. Just shocking the brain by it moving inside the skull when the moving head suddenly stops on hitting the ground will do it. Head injury sufferers, often have radically changed personalities afterwards. You don't want that.