You really need the little propeller that circulates the water. Plus an element that can keep the temperature within 1/10th of a degree. I see a lot of gadgets, like the Instant Pot, that claim to do sous vide. They don't. Accuracy plus or minus 10 degrees is not sous vide. Even though the definition of sous vide means "under vacuum", the cooking technique requires precise temperature, achieved by being in a water bath controlled by a precision instrument, where the water is circulating to maintain that precise temperature throughout.
You should just buy the sous vide stick. These things used to be much more expensive, but are very affordable now, and well worth it. Sous vide often pushes the limit of low temperature cooking for very long periods of time, so if you do not have temperature precision, you could be seriously risking food safety.