It would be nice to see how the roots look like. As for ratio, I just eyeball it really, as gritty coarse I can do it, since my plants are outdoors. Typically you would want to repot depending on the size of the root ball, so it is not getting too long to get dry as well. I prefer using shallow containers with drainage holes.
Sometimes too at this time of the year, the plant is starting to transition from winter to spring, depending on your location, so it will continue to drop lower leaves, and keep just enough. Then new leaves will begin to sprout. But till then, better make the media as porously well draining.
