I am several years aftee the sign-up. When I was approaching Medicare, I began looking into it and was absolutely floored as to the complexity of choices, as you've discovered. It eventually boiled down to A+B+supplement +D. Every year, I still need to spend a large amount of time going through the various part D plans (prescription) offered. It makes a huge difference as to what my wife and I will end up paying during the year for medicines. We boht have different part D plans because we take different maintenance meds, and that makes ALL the difference. And it changes every year.
As someone who retired from a high tech career, and who used higher math on a daily basis, I cannot even imagine how "ordinary" or "innumerate" people manage to get it right. Especially with the constant blaring of Jimmy Walker and Joe Namath to call now and get hooked up with a plan that not only has no premiums, but pays extra back into your SS check. Those may work if you're healthy now, but, will bankrupt you if your health begins to fail. And, as an extra added bonus, if you sign up for them as your initial selection going into Medicare, you may not be able to get back to the original structure of A+B+supplement+D.