I got the Mazda OEM rubber floor mats for all 3 rows of my 2016 CX-9 (parts 0000-8B-M34 and 0000-8B-M35). Price was $142.94 with free shipping and no tax. I am quite happy with them. I had a slight issue with the 3rd row mat bunching-up whenever the 2nd row seat was moved backwards, but after fine-tuning the mat's position the problem seems to be solved.
I initially tried to install the rubber mats over the original car mats, but that does not work in the front row because the mats have to be secured in place. Stacking also does not work well in the 3rd row from a clearance point of view. Not really an issue, just need to find a place to store the original mats now. These Mazda mats do not have the 'tray' design that the Weathertech mats apparently have (from looking at prior posts).