I looked at a lot of different things for math, and honestly did not find anything for K, early 1st, that I thought was much more than busywork. It just all looked to me like the stuff that little kids simply pick up, if they don't already know it.
That said, we started with Singapore Math 1B, when dd1 was about 1st grade age. We've stayed with Singapore Math since then, now on book 3A. We both like it. No trouble at all starting with 1B instead of K books and even 1A. Fwiw, I've found the Textbooks to be more than enough practice, and don't bother with the additional workbooks. There were some concepts early on that seemed to give her a little trouble, and in those cases, I assumed it was a matter of maturity, and we just went back to later, after several weeks or months, and then she caught on with little effort.