I am renting my studio during this summer. It is located next to Montparnasse train station, very well connected to several metro lines and buses and 30 min walking to the Eiffel Tower.
It is a 22 m2 studio with a small kitchen, full bathroom inside and on the ground floor what is very comfortable if you have big bags.
Although it is not a recently renovated studio, It will offer you a pretty comfortable and private staying without need to pay a lot of money.
Super safe and non expensive restaurants