You say you have a smooth hole. If you have that you already have the sleeve, I believe. The 64 dollar question is Does your expandable plug, the kind that someone earlier described as a "lever on it", fit tightly into the smooth hole when the lever is operated. The answer to this is either yes or no. If the answer is yes, then your leak is somewhere else, not through the plug or its mating to the existing sleeve and you do not need to add another sleeve. If the answer is no, then you have mismatch between your plug and the existing sleeve. The mismatch can be a plug too small or a sleeve OD too large.
The expandable plugs are designed to be shoved into the right diameter smooth hole, and when the lever is operated, will expand to seal from water entry. They don't screw in. They are cheap, and all are the same size as far as I know, at least for fresh water outboard sized hulls.
If it does fit tightly you don't need a sleeve at all. But if it fits tightly and the boat still leaks, then the leak must be coming between the OD of the sleeve that is already in there and the boat hull, through gaps in the cobbled epoxy job, most likely. (or have you considered it's coming in somewhere else having nothing to do with the drain hole?) If the leak is between the existing sleeve and the hull, then the black fitting shown above, with the proper prep I mentioned before, should work. It utilized a threaded plug with an O ring, you can see that in the picture. It's housing must be water tight to the hull, which is what I tried to say before.
To repeat, the first question you have to answer before going any further is: Does your plug fit tightly into the existing sleeve? You cannot sidestep this - it has to be answered. Yes, or No. If unclear, come on back and we'll work on it some more.