Next time you can try lying flat on your back in even less water depth, let’s say around the belly? Try keeping afloat by focusing on your breathing (you can look up inverted breathing), and when you feel like you’re dipping too much, your legs can always correct course by contacting with the floor. It depends on your morphology, but arms extended up and hands above your head works well for me (the position babies sleep in). Then tilt your head backwards a little, chest puffed, let your back arch naturally. That’s my method, you can try it