2 stars hotels in Paris?

Check sites like Booking.com, Venere.com and Hotels-Paris.fr You can narrow your search to 2 star hotels and check people's reviews. Tripadvisor is also a good site.

There should be no problem with you staying with your GF

Paris is a relatively small, compact city. The Metro makes getting around fast and easy - you are no more than a 10 minute walk from any station, either. This makes it easy as the further away you get from the Seine, the cheaper the room rates but can still get to the Louvre or the Eiffel Tower relatively quickly

there are quite a few sites that you can search that will likely show you great hotels at the best prices available. check out the website BookMe and you will be able to compare prices on all the reputable travel sites in just a couple minutes. it's very convenient and will save you a bunch of time and money. Also, make sure you buy them online... otherwise they charge much higher fees for phone orders. good luck.

For hotels in France, more important than stars is your proposed budget in euros. The French star system is based upon a hotel's meeting specific quantifiable criteria and has nothing to do with price or comfort.

To simplify your search, I recommend you limit yourself to hotels in either the 5th or 6th arrondissements and when possible deal directly with the hotel yourself by either calling the hotel directly or using the hotel's website (not a third party booking site). To narrow your search, you might want to try here:

http://www.tripadvisor.com/Hotels-g187147-Paris_Il...

Maybe check a hotel website. . . I'm sure that they will tell you there :)