Dear Tryphon:

Well, we know for a fact that the 1st Century Christians did not teach soul sleep. We have an extant letter from Pope St. Clement, the third successor to St. Peter, who wrote in A.D. 97:

But not to dwell upon ancient examples, let us come to the most recent spiritual heroes. Let us take the noble examples furnished in our own generation. Through envy and jealousy, the greatest and most righteous pillars [of the Church] have been persecuted and put to death. Let us set before our eyes the illustrious apostles. Peter, through unrighteous envy, endured not one or two, but numerous labours and when he had at length suffered martyrdom, departed to the place of glory due to him. Owing to envy, Paul also obtained the reward of patient endurance, after being seven times thrown into captivity, compelled to flee, and stoned. After preaching both in the east and west, he gained the illustrious reputation due to his faith, having taught righteousness to the whole world, and come to the extreme limit of the west, and suffered martyrdom under the prefects. Thus was he removed from the world, and went into the holy place, having proved himself a striking example of patience.

It was not uncommon in those days to refer to death as "sleep". Even today we may say that to a little child. But, Scripture clearly tells us that we are immediately upon death brought to judgment (the Particular Judgment), and then are sent to heaven (Purgatory) or hell to await the Resurrection at the end of the age.

(2 Cor 5:6-8)  So we are always of good courage; we know that while we are at home in the body we are away from the Lord, for we walk by faith, not by sight. We are of good courage, and we would rather be away from the body and at home with the Lord. 

There is no mention of soul sleep here. We are either in our body and away from the Lord, or we are away from our body and with the Lord.

When Jesus was on the Cross he told the thief that he would be in paradise that very day:

(Luke 23:42-43)  And he [the thief] said, "Jesus, remember me when you come into your kingdom."  And he [Jesus] said to him, "Truly, I say to you, today you will be with me in Paradise." 

St. Paul teaches about purgatory in 1 Corinthians 3-11-15. How can we be in purgatory if we are asleep and will not awake until the Great White Throne Judgment when Jesus returns. 

For no other foundation can any one lay than that which is laid, which is Jesus Christ. Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, straw—each man's work will become manifest; for the Day will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. If the work which any man has built on the foundation survives, he will receive a reward. If any man's work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.

The Final Judgment at the end of time is preceded by the resurrection of all men. Our souls are reunited with our bodies and then the Judgment comes (Hebrews 9:27; Acts 17:31). After that Judgment we go straight to heaven or hell:

(Rev 20:11-15) Then I saw a great white throne and him who sat upon it; from his presence earth and sky fled away, and no place was found for them.   And I saw the dead, great and small, standing before the throne, and books were opened. Also another book was opened, which is the book of life. And the dead were judged by what was written in the books, by what they had done.  And the sea gave up the dead in it, Death and Hades gave up the dead in them, and all were judged by what they had done.

Then Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire; and if any one's name was not found written in the book of life, he was thrown into the lake of fire. (cf. Mt. 13:30; 47-50)

Jehovah Witnesses and other have to run all sorts of intellectual gymnastics and dishonesty to mangle these and other verses to proof soul sleep.

For more detail see the 1910 Catholic Encylcopedia articles:

Particular Judgment
General (Final) Judgment

God Bless,
Bro. Ignatius Mary