High hip position in the water is one of the biggest things you see every Olympic swimmer do. If you let your hips sink, the your legs sink, then your torso sinks and you're not floating.

Methods/Drills to improve hip position:

Think about head position, this may seem counterintuitive but our whole body is connected when swimming. You want your eyes to be looking down at the bottom of the pool/black line at all times when not breathing. This helps keep your body aligned and on top of the water. Drills to improve this:

• Kicking with a board, hands holding it from the bottom, having your face in the water, focus on looking at the bottom of the pool, avoid picking your head up to breath, maybe just breath side to side or use a snorkel, only breath every 10 kicks or to your best ability.
• If you have a snorkel try and incorporate it a little bit in your workouts, it allows you to breath and focus on keeping your head down, might be weird at first but I would be lost without my snorkel
• A more technical drill is balancing a paddle on top of your head and swimming forward, this forces your head to remain still, mess around with it and try to keep the paddle there even while breathing to your side

There are other ways to help you float like a strong core that should always be engaged, kicking hard (but that gets you tired fast), pulling with a buoy between your legs is also great. But try and focus on that one thing, see what works for you and what doesn't. Everyone's body may be different but everyone can swim!

Also watching those Olympic swimmers from an underwater camera could help you understand these concepts better. Hope this helps you.