The Penguin Classics line is sold through Kobo and generally quite good. They were the editions that one of my literature classes used. You do have to check the table of contents to make sure that the one you get actually does come with an introduction and notes because Penguin also sells non-annotated e-book versions. They are somewhat pricey, though, especially for the less well-known works, and rarely go on sale.
The ones with the picture covers with the white banner and a black background for title/author info such as this one,
The Pillow Book of Sei Shōnagon, are the kind to get. But some newer ones are showing up as the "Penguin Classics Deluxe Edition" with covers that don't have the banner, such as
Kristin Lavransdatter.
Linkage for Kobo for the
Penguin Classics imprint, the
Penguin Classics Deluxe series. The cheap ones in the
Penguin Little Black Classics line seem to just be single stories/essays excerpted from longer works, and don't appear to have the notes.
NB: not all of the Penguin Classics are filed under the dedicated imprint or listed as part of the series search at Kobo.
If you were able to easily buy and strip books from B&N, I'd have recommended the
Barnes & Noble Classics series, which are really very well done, and affordably priced at $3.99 USD each (they used to be $1.99 USD years ago, but then they jacked up the price).
They gave away quite a lot of them years ago in a promo, and they usually contain an introductory essay for the work, an introductory essay for the author, a timeline for the author and other important events related to the work during their life, sometimes another essay or two for some aspect of the work and author, and then a lot of both endnotes explaining cultural backgrounder stuff and footnotes explaining things that happened within the book and then, depending on the book, sections about reception of the book at the time or its lingering influence (quotes from old reviews, generally, but sometimes an additional essay), study group-type questions, and sometimes recommended further reading (biographies of the author, studies of the book, websites, etc.).
They used to give away 3 free when you signed up for a B&N account (
Dracula, one of the Jane Austen novels, and
Alice in Wonderland, I believe it was), but I don't know if they do that any more, and it would probably be far too much of a hassle for you to obtain them anyway. But they really are very well done.