A "secular/purely philosophical religion" is almost a contradiction in terms but if I were to guess at what you mean by it, I would suggest something like "a rational philosophy to live by" as opposed to a religion, which provides a moral framework but may not be very rational, or western philosophy, which is rational but doesn't provide much moral/ethical guidance.
If that's where you're heading, Daoism may be a disappointment. The Dao De Jing (various spellings!) is lovely but Daoism has splintered and morphed, much as Christianity has. You are most likely to find Daoism as a current within Chinese folk religion or as the theoretical underpinning of practices like Tai Chi. Keep looking, by all means, but don't be surprised if the results are ... 'untidy' might be the best polite word.
Other places to look might be the 'sceptical Buddhism' movement (e.g. ) and 'secular Humanism' .
You may also get some clues in the thread here on Stoicism, especially this post , if some fairly technical language doesn't deter you.