Oh, lucky you. I lived in Paris for 4 years before dcs and would LOVE a weekend there with just dh.
Gare du Nord area, as with those around most big stations in large citiies, is pretty scummy. Depends on your budget and what you're likely to be doing which arrondissement you'd be best with. If you want to save your money for nice meals/buying Christams presents, stay somewhere round there - prob recommendations on Eurostar website - and get a taxi back at the end of the night.
If you like the oldest stuff near Notre Dame, try Hotel Esmerelda - very very old with squinty beams and comedy-shaped rooms; not v pricey but not glamorous, just v characterful: you wouldn't forget the stay.
Hotel de Varenne is near Eiffel tower and OK location for strolling along the boulevards Saint-Germain and St-Michel but more expensive.
Paris Time Out is usually reasonably honest about listings so I'd try the website first. The 4th arrondissement is also v old and characterful and I know there are lots of small places there, just don't know the names.
If you can say a bit more about what you're looking for to be nearby, I can be a bit more helpful about areas to look at.