"Cosy," stateside is used euphemistically by realtors stateside, but could not be more accurate here. The flat's more pied a terre than apartment, but it's fully modern, smartly laid out and personally decorated that you may question how long you could manage to live there--but you'd want to try anyway.
It's in a courtyard off a major road; you can hear sirens and footsteps from the neighbors but not much else. 5 minutes in either direction gets you to the Métro or RER (40 minutes to CDG, 20 minutes to Gare du Nord), 10 minutes (on foot) to the north puts you in reach of several extraordinary bakeries, cheesemongers, butchers, and an open air produce and vintage market; 10 minutes to the south and you can picnic on the Seine. The kitchen is well equipped if you want to cook (and you should consider it), there's a washing machine under the countertop and a drying rack in the bathroom. Other than a spectacular balcony, I can't imagine a better base of operations for a trip to Paris.