The Loeb Classical library series will have what you need for Greek or Latin texts. The book will look like this more or less, with original language text on the left and translation on the right. Loebs can only be accessed online by those with institutional logins (or if you pay, of course), but you can buy old Loebs very cheap from online sellers like abe books or in used book stores. Iliad comes in two volumes, and Critias comes bundled with some other Plato diaglogues: Timaeus. Critias. Cleitophon. Menexenus. Epistles. If you are near a University town of any size, you can probably find an Iliad loeb in a used book store there. The Plato volume will be more tricky, but you can definitely just order it online. Note that there are older and newer versions of Loebs. Try to get a more recent edition, as the translations are generally better.