I use the book called Suomen Mestari.
I have used in the past books called Finnish for Foreigners and other grammar books to support my students studies.
To order the book, the quickest and safest way has been using Amazon. I have zero connection to the writers or publisher (Finn Lectura). I do not get any commission by ordered books and I also order my editions from Amazon. (Just to avoid confusions)
I have seen many efforts of a “good Finnish language book” in these six years I have been teaching, but so far this monolingual has been the winner. Mainly because it doesn’t try to explain Finnish grammar through English grammar. You know, not all the English speakers paid attention their grammar lessons at school. So this book forgives that and offers a chance to learn.
The newer edition of the book is of course better, but if you still have the older edition, we will make it work on your lessons.
HERE IS THE LINK TO FINN LECTURA