For my upcoming Murderhobo Remix scenario. These light-eating space plankton are almost the size of horses, they levitate along (albeit slowly) and can carry amazing loads. They are quite stupid, but docile and obedient. The main trick to teach them is to land, so you can mount. Otherwise there are hook harnesses that go into the eye creases, to pull them one way or another.
It is difficult to imagine what riding a space plankton would look like, so I drew a picture.