Not OP but I have the same or similar issue. Filling your lungs is pretty easy to try and pretty much the first thing that comes to mind and almost always the

Not OP but I have the same or similar issue. Filling your lungs is pretty easy to try and pretty much the first thing that comes to mind and almost always the first suggestion everyone gives. I've done a lot of lap swimming, sub 30s 50m, can hold breath for ages, swim 50m underwater, comfortable scuba diving etc but that doesn't help. The issue is not total flotation per se. It is balance. I can't push air down into my legs, so they go down. I have then lost a lot of surface tension with my body area, so I go down. I end up vertical but with max capacity lungs I can bob near surface. But breathing out to breathe fresh air in makes me go down. Compared to someone floating happily on their back it is not relaxing. I really wish people would give up on the "eVeRy0ne cAn f1oAt!" idea. With just my body(IE no floating aids/neoprene), nope. What I do instead, I kick gently. Just enough to keep my feet up. That keeps the rest of me up holding surface tension. I'm pretty sure I could do this for hours if need be but never want to be in a position for survival to know.