Rue Rivoli and the heart of the Marais is a wonderful part of Paris to stay in. The center of the Marais is a lively neighborhood with a strong alternative lifestyle scene as well as lots of trendy bars, shops, and restaurants. The rue des Rosiers is a centerpiece of Jewish lifestyle in Paris and the Ile St. Louis and the Ile de la Cité are the oldest parts of Paris.
Rue Roi de Sicile is a street that runs parallel to Rue Rivoili (main street with most of the shopping, Louvre etc. runs into Place to Concorde if you venture to walk). Sicile tends to be less busy than Rivoli - there are lots of great little places to explore there.
Downside can be that it is so lively - This is a heavy visited area - you may find shops may speak a little English as well as restaurants - but this is an area to also be streetwise.
I love this area - we meet here from Sunday brunch and take a Velib to ride once a month.
Your main Metro line will be #1 - but try bus 72 from Chatlet