well i was a frequent traveller to paris alone and being an 18 year old female i needed somewhere cheap but safe, i have stayed at two hotels whilst arranging to move here (paris) hotle notre dame de lorette (type into google there is a website) which is quite cheap and lovely, a little small but as you are on your own its perfectly big enough. also only like a minute from the metro line 12 which takes you to the majority of main places easily!
also there is another one in paris in the 7th arrondisement a bit more expensive but its in one of the safest arrondisements, hotel eiffel rive gauche, again there is a website if you type it into google.
i booked both of these hotels on expedia and had no problems at all, the staff in both hotels will speak english and help you in any way they can.
hope you have a great trip, obviously im a little biased by living in paris, but it really is fabulous and the only tips on safety i can offer which have worked for me are to use a bag that will go across you body or tightly under you arm and never get the first or last metros, they are very weird, i was glad i was with someone when i did that. ENJOY!