Nicole,
after 5 knee operations, I no longer kneel to get my low shots. I either set up my tripod low with an angle finder or I sit on the floor. I've tried gardening stools, pillows, creepers but I find that scootching along on my rump works best for me. On the other hand, getting your subjects off of the floor is probably the better solution long-term. All but the largest dogs can handle a modeling table that's 2 or 3 feet off the floor. In my previous studio, I built a platform that was 18 inches off the floor and put my props on that. It gave me just the added height I needed to be able to sit in my office chair for the shooting. The one basic truism of portraiture is that if you or your subject are in pain, it will show up in the images .

Jim