Yeah, do it only with your fingers and a stiff wrist.
Rather very relaxed wrist but locked hand position (important that although the hand is locked in position, it is tension free)
That can't be the case. A 'locked' hand position will require constant tension no matter how 'slightly' it's done. Better to only lock for the moment of key depression then instantly unlock.
Obviously there are more than one technique. I have a tendency to not agree with KeyboardClass, but I know some people who would agree with him, and they are doing just fine.