Look at the liner notes of the albums you already own and track down those writer and performer influences AND track down others who have performed those same songs, like was suggested above. Your taste will shift (broaden) as you listen to different renderings of the songs, and if you listen to each performer's other works and look into their other influences, you'll experience an exponential growth in your knowledge of songs and performers.

Once you have a list of folks you want to investigate further, consider visiting your public library to find their CDs or albums available to check out (and don't forget about Interlibrary Loan if they don't have what you're looking for). This way you can explore many but invest in those that really catch your ear.

Good luck!

SRS