Rav Baruch Ber was well known that when he had to yell at a talmid, he first went to his office, composed himself, put on a special “yelling hat”, and then first yelled at the talmid (if it was needed).
May I suggest a similar concept for physical discipline. If you feel it is needed, wait some time to “calm down”, put on a “special” piece of clothing (might I suggest an “A-shirt”), and then explain to the child why they are being punished.
After all that, if you still feel the child needs to be punished physically, then at least you know you are not doing so in anger.