Certainty in science is associated with such concepts as level of significance, error, deviations from the norm, randomness, etc. I don’t think that is what you mean.
If I understand you correctly, you seek to know beyond a doubt. I am not sure this exists outside the actual Beatific Vision. Even if you were to have a glimpse of it right now in time, it would just as quickly be gone and you might later wonder if you had been hallucinating. Probably not but let’s say that doubt is to faith as death is to life. It may be a form of self-abuse, a temptation of God to be undermining one’s own faith.
Interestingly, you are holding yourself as the final arbiter of truth. You seem to have taken that big step without appreciating what that means. Isn’t this amazing?!? - not only the very existence of oneself, but the ability to know. Even if we conclude that we exist in a state of ignorance, it presupposes a capacity to know truth - to awaken to the Truth, to accept its revelation.
Back to the OP. I am sure that your entire life, you have sought to live (in desperate moments one mourns the loss of fullness of life); you have sought what is beautiful, what is good, what is true. You have looked for love. Side-stepping a lengthy discussion, I will simply say that your entire life has been a search for God.
In reply to your question above, I would say pray, read scripture and other sources provided by the Church, behave in a charitable fashion, giving of yourself to others, participate in the mass and the sacraments. Clearly there are other paths, but this is the fastest and surest way to get to where you want to go.