If all men are tainted by original sin, then we can only hope to reach TOWARD our salvation as best we can, if we choose to do so.
If you are looking for ABSOLUTE ASSURANCE that you have PERFECT INFORMATION about that which you seek, then you deny the necessary existence of “mystery”, and the unknowability of certain things, and your reliance (ultimately) on faith.
There is no absolute assurance about anything, other than in faith.
Therefore, the only alternative is to strive to do the best you can, and have faith that god will give grace to him who does so so as to grant him salvation.
To despair at the realization that you must rely ultimately on faith and not your senses (which is an idolatry) is to not REALLY believe that which you profess as a Catholic.
Who would you trust to answer the question “Who teaches with authority?”
Would you trust the person who answered you?
Why?
Just as you trust the “early church” to have been informed without error,… you must trust that you are being informed by a trustworthy source, to the best of your discernment,… which means that ultimately you must trust in the holy spirit to do the informing of both yourself and your “teachers”.
So,… once again,… it comes down to “who do you trust?”
What is you answer?