This year in university I took a course where I had to imagine creating a startup and we ended up mocking up an agritech business that dealt with drones and satellites data. We discovered that Sentinel 2, a European satellite, has a resolution for ndvi that goes as low as 10/20m. This improves nasa's modis sitting at a resolution of ~250m.

Furthermore, this is free. There are companies providing paid images with higher resolution from their own satellites (Constellr comes to mind). I'm sure the resolution isn't going to be exact to the square foot, but for some cases you probably don't need such a high resolution