I was in Paris just for a week end and the Xavier's flat is perfect for me, almost in the middle of Paris, perfect connection to everywhere with the metro not so far from Louvre and Orsay ( about 20 mins by feet ).
Xavier is a perfect host and the check in is well organised ( you will get from him all codes to going to the flat.... yep, seems " the da Vinci code" movie :-D ) and if you need anything Xavier is there to help you.
last suggestion , the "pain Quotidien" bakery in the corner is very nice