My rate requires a Class II swim test and this video goes over that, however, the prone float is what you'd be expected to do even if you're not taking the Class II swim test. It's towards the end of the video. It helped relieve some worries I had regarding the prone float as well because I tend to sink. But the form that the sailor does in the video actually helps. I've been swimming for months while in DEP.
https://www.youtube.com/watch?v=-gIrh2xJJ5E