I know no helmet will protect you in more serious knocks so I'm looking for the lowest profile that fits me well.
You're wrong about the serious knocks. That's what helmets are designed to do. Prevent severe injury from serious impacts. This level of protection ultimately means the smaller knocks aren't serious at all. A good helmet will save your life from serious knocks to the head. A helmet with reduced profile may not be able to absorb as much impact energy, it may not have as much coverage down the back of the head. Yes, you can still die from head trauma while wearing a helmet, that's true. It's just less likely and impacts need to be much greater.
The other thing is helmets reduce concussions. They aren't designed to prevent concussions.
I'll give you two real life examples in my life. They are bicycle related, but the technology, design, and impact speeds and fundamentals are similar.
Five years ago June, I was sitting at work when I got a phone call. My friends father was being life flighted to the local hospital in critical condition. I learned this when I got there. Coming down a hill with a corner in a group ride road bike ride, he hit some gravel. He slid across the road and hit a tree square to his back. The impact broke his vertebrae damaging his nerves while causing severe internal bleeding. He had a major concussion when the back of his head hit the tree as his body wrapped around it, but no bleeding in his brain. We estimate he hit the tree at 25-30mph. The trauma surgeon said he would have died at the scene if he wasn't wearing a helmet. One year later that bad ass was back on the bicycle.
That's an effing serious knock to the head.
Second story. While mountain biking I went over a rock feature on a nice dry day. Turns out those rocks had moss on them that made them as slick as East Cost snow. The bike went out from under me and the side of my head hit the edge of the rectangular cut rock. 1/4" dent into the 1/2" foam. I was only shaken up. Doubtful I got even a minor concussion. Wearing a helmet turned what would have been a serious and bloody concussion from impact to the side of my skull into a loss of $50.
Best $50 I've ever spent.
Just make sure the helmet is certified to ASTM 2040 / CE EN 1077 and has good coverage on the side and back of the head. You wear a helmet because it will save your life. It also happens to keep your head and ears warm better than a beanie. You don't buy a helmet because it looks good.