How can I add my son to my house deed as a transfer on death in case anything happens to me?

First, read this.

A "transfer on death" deed is not legal in all states. This site indicates that it is only available in Missouri, Kansas, Ohio, Arizona, New Mexico, Nevada, Colorado, Arkansas or Wisconsin, while this one says it's no longer available in Ohio.

You might want to convey the property from yourself to you and your son "as joint tenants with the right of survivorship", if allowed in your state. Unlike a "transfer on death" deed, half ownership is conveyed at the time of execution of a JTWROS deed.