I like Singapore Math , specifically Primary Math US Edition, which is the oldest and most Singaporey version. It is also the cheapest, and the one which you are most likely to find on the used market.
Levels are split A,B - thus you'll have Textbook 1A /Workbook 1A and optionally the Home Instructors Guide 1A, and then move on to 1B, then 2A, then 2B, and so on.