My answer, having thought about it is that I don't know and am not sure that morality is a fixed enough "thing" to have an ultimate morality. I think that "do as you would be done by" is a fairish place to start also "An it harm no one, do as you will"....also "do your best"
Your own conscience dictates your morals according to your culture. Many simply have no conscience, we refer to them as scum. They refer to us as mugs.
The desire to do what is right follows from knowing what your options are, how to fulfill them and understanding the ultimate consequences of your choices. Extra points are not awarded for the failure to acknowledge personal responsibility.
Yes, God is the ultimate authority as His laws are absolute.
Those who believe in the culturally defined standard for morality are faced with, to give one example , if say in 50 years time 95% of the population think pedophilia is ok, then by definition it will be ok
It won't be long before, (after abandoning Gods laws completely), we shall see, not only LBGTQ etc, but many many more sexual identities, and, "marriage," between who knows what and how many? It will put the Mormons to shame as,"new marriage," with no overarching authoritative norm, becomes like something emerging from the jungle.
Many years ago, divorce was frowned upon, and living together unmarried was shocking as was being born out of wedlock.
How times have changed as God has been pushed out of public life.