Oman is fantastic and the Al Bustan Palace (which is part of IC) is wonderful, although I havent been there since the refurbishment.

The only problem is January is when they get the most rain (albeit not huge amounts). From my experience (and having lived in that part of the world) it can also verge on the chilly side (meaning it certainly cant be classed as hot). We recently visited in early December and there were some cooler and wetter days then too.

Mauritius is lovely too, but Feb / March is cyclone time, iirc.

Whichever you choose I'm sure you'll enjoy!