A Namor marriage would be pretty awesome. If handled correctly.
However, right now the only lady I could see Namor actually benefiting from, who isn't a new character, is Storm. Both Namor and Storm are both characters that would benefit being pulled throughly out of the boxes they have been written in todays Marvel Universe. With Storm at Namor side we would get a woman who could challenge him and bring out Namors more gentle side, while at the same time would allow him to be ferris when he needed to be. Storm on the other hand would benefit from getting a door way to multiple areas of the MU. Avengers, Defenders, Invaders, you name it Namor has some connection to it in some form or fashion, which will allow the transition to be easy. And she would get the added perk of being Queen. But thats just my opinion.
It should be noted I only ship two couples in the MU. Namor and Storm . Iron Fist a.k.a Danny Rand and Phoenix a.k.a Jean Grey, with this one solely due to the Chinese legend/myth of the Dragon and Phoenix in Chinese culture. I felt like I should clarify that, so I don't look like a crazy shipper person.....I'm not helping my case though so I'm going to stop typing now.