The notion of ethics and morality is, in part, like language and medicine - it evolves according to need and is reduced according to necessity as progress renders aspects of it irrelevant.
But fundamental ethics revolve around life and sustenance and unless other mechanisms are ever established to artificially substitute for what is currently required to maintain those needs, ethics and morality will be founded on them within a functioning democracy!
But absent any god, the ways in which a democracy establishes codes for human behaviour is very much down to the individuals!
A harm none umbrella seems an excellent foundation!
Beyond that, behaviours being engaged in which employ the highest degree of self protection to help maintain whatever is to become a lifestyle choice - would seem a sensible guideline!
And so morality and ethics ought not to be so interwoven with what is evil/good or labelled disgusting or contemptible purely due to anothers religious indoctrination, but far more about shared ideas and shared values and shared life experiences which help reduce harm and promote sustainable interaction and enjoyment of life!
The above is what I would generally hold in mind in establishing any moral code from a base of zero and attempting to do so by completely losing all previous indoctrination as to what constitutes morality!