There is a whole genre of older textbooks, now out of print and freely available on Google Books and elsewhere, that aims to provide straightforward Latin with vocabulary and idiom help on the page. Some of these books, especially Post's, have excellent advice on how to approach sight reading and develop the skill of reading at sight:
Post, Edwin, Latin at Sight (Boston: Ginn & Co. 1895).
Franklin, Susan Braley, and Ella Catherine Green, Selections from Latin Prose Authors for Sight Reading (New York: American Book Company, 1903).
Janes, Arthur L., Second Year Latin for Sight Reading: Selections from Caesar and Nepos (New York: American Book Company, 1911).
D'Ooge, B.L., Easy Latin for Sight Reading (Boston: Ginn & Co., 1897)
Beeson and Scott, A New Second Latin Book (Chicago: Scott, Foresman & Co. 1916).
Gleason, Clarence W. A Term of Ovid: Stories from the Metamorphoses for Study and Sight Reading (New York: American Book Company, 1920).
R.C. Jebb, H. Jackson, and W.E. Currey, Translations, 2nd ed. (Cambridge: Deighton Bell & Co., 1885). Passages for sight reading selected for "the needs of young students" and used in classroom settings in Cambridge. Both Greek and Latin. Includes English translations.
If you are looking for plenty of Latin passages of all levels of difficulty to try, look no further than the Packard Humanities Institute's library of Latin texts. These are high quality texts, beautifully digitized, and now available absolutely free. Thank you, PHI!