Hi Scuba Stan,
Sheraton Full Moon resort has a diving center on the island, run by Euro Divers. Is there any reason to not dive from right there?
In January, we are in the Iruvai Monsoon season, where winds come predominantly from the northeast, and the main oceanic current goes east to west. What this means in terms of diving is that on the east side of any atoll there will be mainly strong incoming currents, with great visibility, but also potential for rough conditions on the outer reefs, caused by huge ocean swells. On the west side of the atolls there will be mainly outgoing currents, with less visibility. The mantas, by the way, usually hang out in the outgoing current side, so they will be easier to find on the west side of the atolls during the Iruvai monsoon (what is commonly called the dry season), while in the Hulhangu monsoon (the rainy season), they are easier to find on the east side of the atolls.
Sheraton Full moon resort is on the east side of the North Male atoll, so if you decide to stay in that area for diving, you will have the nice viz and strong incoming currents. There are some great drift dives in the area: Furana North, Club Med Corner, Lankan reef, Aquarium, Middle Point... all on outer reefs. For me these are great dives, but you need to like currents

The small thilas inside the atoll might be trickier to do if the currents are strong: usually dive centers will take only experienced divers.
The reason why many liveaboards go to South Male atoll during this season is that there are some great kandus (channels), where you can do some thrilling drift dives.
If mantas is what you want to see, then move over to a resort closer to the West side of the atoll.
(I myself am based in Thulhagiri, in the middle of the North Male Atoll. Will gladly give you more info about the area & resort if you wish)