I should also mention, this non dual awareness practice is used by Christians (See Cynthia Bourgeault), Buddhists, Hindus, Sufis, Jewish mystics, AND atheists.

it's the basis of Sam Harris's Waking Up series, and he is most devotedly an atheist. So anyone can use it. But you're right - the over thinker would probably do better with a focusing technique to start, and your other suggestions for different types are excellent as well.