I've never been remotely religious, but, I do suspect that religion provides an illusion of security, that atheism can't. In that sense, I don't expect atheism can make you as happy.
I'll be honest, I was happier when I had religious faith. Sometimes I wonder if religious faith can be captured without actually having religious faith?
Maybe if I were to invent a God and pray to it. Would this bring any happiness? The God wouldn't be real. It would kind of like an imaginary friend.
But when people have sex fantasies the other person in the fantasy is an imaginary friend too, but that doesn't detract from the pleasure they bring. In fact, if you stopped in the middle of doing the deed to tell yourself that this person is only imaginary, you'd ruin it.
Would an imaginary God work in the same way?
Take a look at other people, who believe 110% in what they're doing. They're also happy, content and satisfied. It's not religion itself that makes people happy, it's having the belief and conviction that what you're doing is right, and that it's not only helping you, but also helping society, even if in the most minute or trivial way.
I would even go as far as to say, as someone else on this forum has said, that an atheist can perhaps have a more happy, successful and fulfilling life than any religious person: only an atheist can appreciate, totally for themselves, what a wonder the Universe and all of existence is. Atheists don't have to be told to look at the creation of some all powerful creator. Atheists don't have to be told to be nice to others. Atheists don't have to be told to give charity. Atheists do these things because they want to, for themselves, not for the thought of some reward in the next life, or to pay for sins, or whatever
Good point. There is satisfaction in knowing that you are genuinely searching for the truth, rather believing what suits you best.