Man this medicare stuff is complicated. Here are some notes and tips on:
This is the hospital related. You pretty much always get this if you worked or your spouse every worked it is free. Otherwise you have to pay a premium of $400/month or so to the government.
This is out of hospital. You have to make sure to enroll for this each year, so you have to very sure that your address is correct with the government. This is a real pain, but make sure on socialsecurity.gov and medicare.gov that you can login. I use a password manager for this as I'm always forgetting the passwords. If you do move alot, try to use a mail service so that you have continuity. If you move and they can't mail you things everything really breaks. Normally this should be deducted from your social security.
This is the drug coverage. You get this from a third party provider but the government may also bill you for an income related surcharge. Make sure that you have medicare autopay up and running so it doesn't die on you. If you don't pay the supplement you will lose part D! So Part D has two people you have to pay, your insurer and the government. You can contact your plan to get your Part D deducted from your social security.
And here are some important hygiene things:
Keep a government issued id
This doesn't seem important but even if you don't drive anymore or don't travel, you want to keep your passport and your drivers license up to date (you can usually get some sort of state issued identity card). This you need to authenticate in the modern world.
Use a password manager like 1Password
Because you will forget these myriad of things as you only logon once a year and they require lots of authentication. I use 1PAssword. Give the codes to a trust child or someone younger so that it always is around because losing your passwords in the modern world is terrible.