All right, I'll make it short, but here is MY truth.
Atheists, might or might not be happy, but they lack something that others have, and that is spirituality. Spirituality is a need in human beings, okay? okay.. so what I'm saying is, pick a religion, and here is why:
There is no truth, truth is absent, the definition of truth, is what people commonly accept as true, before, in Medieval Europe, the truth was Christianity, and that is it, period, they were as sure as you say, the America flag is red white and blue... Well, I say, it's just a green dot in a white background.... That's the truth.
You see, you need to get out of your philosophical comfort zone, and actualy retrospect about this issue, there is not truth, so why not pick in a beliefs, that will give you life meaning, and that "might' be true, not like worshipping a banana, but something that a lot of people believe, or that your ancestors believe, or your own belief!
Sipirituality makes you healthy.
May peace be with you.