Try The Suttas there are five collections, the Digha Nikaya, Majjhima Nikaya, Samyuta Nikaya, Angutara Nikaya, and the Kundhaka Nikaya.
I am not sure how many volumes these take up in total but I will guess somewhere around the 30 mark? but there is also the Vinaya or Abhidhama which have 12 volumes between them. I think the full collection spans about 5foot of shelving.
but if you are looking for an introduction to Theravada texts try "in the Buddhas words" by Bhikkhu Bodhi, or "Wings to awakening" by Thanisaro Bhikkhu (the latter is freely available on-line)
if you are looking for an introductory book on Buddhism particularly the theravada then "what the Buddha taught" by Rahula.
He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them.
But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion …
He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form.