I don’t think you should be so quick to reject the possibility that value could be objective. But if you want to go with the assumption that value is subjective, you might want to look at how subjectivists about value have tried to incorporate values into their moral theories.

Some of the disagreement between relativists and non-relativists might be due to a failure to adequately distinguish morals from mores; that is, genuine moral principles from social custom and expectation.

I think it would be helpful if you clarified what falls within the moral sphere and what doesn’t. I worry that you’re position excludes things that should be part of morality, but it’s hard to say for sure at this point.