Hi Milly,
You gave the impression you have not heard enough traditional/folk to help you select a repertoire. If you can manage it at all, I strongly suggest you treat yourself to the Topic labels 20 CD compilation "Voices of the People". This will introduce you many great singers and songs, and comes complete with booklets containing all the lyrics. If you like Scottish songs, have a look at Springtyme.com.site. There are a number of CDs of Festivals in Fife which have many songs you could sample before buying and which have'nt been sung to death.
While some people have suggested Songbooks, (Marrowbones is my own favorite), you will still find yourself wanting to hear a those songs sung, so again, I suggest you get some Cds the come with a lyrics booklet.