HSK Standard Course 1 (textbook + workbook)
Jiang Liping · Beijing Language and Culture University Press
This is the series written by the people who write the exam, and it shows in a specific way: the vocabulary in each chapter is exactly the official list for that level, in the order the test assumes you met it, so nothing you study is wasted. The fifteen lessons cover HSK 1's 150 words with a listening track for each. Buy the workbook alongside it rather than instead of it — the textbook alone gives you very little to actually do, and doing is the part that sticks.
What it does not do: It explains grammar thinly and almost entirely in translation, so if you want to understand why a sentence is built the way it is you will be looking that up elsewhere. The recordings are slow and studio-clean; they will not prepare you for a real conversation.
Free here first: All 150 HSK 1 words, free