This reading order for Stephen King's Dark Tower multiverse lists 11 essential novels, 3 essential novellas, and 4 complimentary bonus novels that add depth but aren't crucial in journeying to the dark tower.

The 11 essential novels are:

The 3 essential novellas are:

The first 2 can be found in the collection Everything's Eventual but are listed individually because the rest of the collection is unrelated to The Dark Tower. The third is part of the collection Hearts in Atlantis which is listed in entirety because the contained stories are interconnected.

The 4 bonus novels are:

These books are complimentary to the plot of The Dark Tower but not essential. The Talisman doesn't really tie in with the series that closely, but it's necessary if you plan to read Black House which does.