You may still want to check the level of difficulty of the material you have chosen. The lower the readability level, the easier something is to read and understand. A readability under about 10 will be able to be understood by most people. One further thought on readability level. Sentence length is also a factor.
Longer sentences are more difficult to understand even if the words themselves are simple.
The problem is the need to remember an increasingly complex structure as the sentence length grows. Lastly, if you are still searching for that elusive piece of material, you could do worse than consult the pages on this site which publish the writing of some of our Students .