I am retired military so basic medicare and Tri-Care for life is about as good as it gets. The whole process is very confusing, and it was very hard to find a clear answer as to whether I needed any supplements. (I don't, TriCare for life takes the place of supplements and prescriptions for me);
In my area there were free seminars on signing up for Medicare. Granted, they were sponsored by insurance brokers but there was a lot of good information and explanations provided about the Medicare system.
One odd fact about signing up. When we were doing our initial application I provided a specific change over date. I had given two month notice at work and new the exact date I would switch to Medicare. That day came and went. A month or so later we went to the doctor and had an issue with the billing. Turns out you had to call Medicare a second time and tell them you really dropped your other insurance. Got a love a bureaucracy.
Get the books from Medicare and start reading now. Some choices, if made wrong could penalize your for a long time.
Doug in SW IA