ECG detection using minimal number of electrodes

Disclaimer: Hello, I’m someone from an electrical engineering background, so this question may sound dumb.

I wish to make a wearable ECG monitoring device for arrhythmia detection. Since the device is to be wearable, it has to be small and should not obstruct normal behavior (kind of like those ECG patch monitors).

My question is, which lead should I monitor for arrhythmia detection. I read that I do not need all 12 leads for this purpose. The leads should preferably involve electrodes close as possible to reduce area of contact with the body.