Well, then it doesn't take any thinking at all, per se, to find out that purpose, does it? But something must modify this, though: morality, right?
It does not need to be modified at all.
If by "morality, right?" you mean moral values, moral values do not "modify," the objective. Values, of any kind, are only needed if their is already an objective or goal. The values tell you what kind of actions will achieve that goal. What kind of actions will "work" depend on the kind of being they pertain to, in what kind of environment (world). But no values change the goal itself.
-- so as to find one's best pleasure? ... the noblest and best set of pleasures?
A teenager might equate "enjoying life" with pleasure, but a philosopher does not. What will actually determine the meaning of, "enjoying one's life," must be discovered by each individual. Within certain parameters, dictated by the limits and potentials of human nature and the nature of the world they live in, there is no way to know what will be appropriate to the fulfillment of each individual's nature. We are all different.
We must all eat, learn, work, discover our potential and attempt to reach as far as we can, but what that means for each, only the individual can know. This is one of the things wrong with all attempts to treat every indivdual in the same way, from education to laws governing safetly and health, for example.
This does not mean a person can do just anything they like, so long as they like it. They cannot take deadly poison into their body and not suffer the conequences. They cannot take mind-numbing nonsense into their minds and not suffer the consequences. A human being cannot live contrary to the requirements of their own physiology and psychology and get away with it. This, too, every individual must discover.
Hank
I don't see anything in your this post, HK that isn't relativism; "law of the jungle" as Alamo-Girl has said. Nothing about not harming others, for instance. It looks more hole than doughnut to me.