There is some misinformation in some of these posts. You can switch back and for the between original Medicare and a Meeicare Advantage plan every year if you want to do so, during the Annual Enrollment Period. The issue is that you would not necessarily have a guaranteed right of issue for a supplement (also called Medigap) as you do when first enrolling for Medicare, and your premium will also be higher for the supplement because the rates are set by age at enrollment. Everyone needs to do their own research each year to decide what is best for them, particularly if you have a prescription drug plan (Part D). There's a great tool for this at
Medicare.gov: the official U.S. government site for Medicare, but the rates and plans for next year aren't in it quite yet. Note, I am a SHINE volunteer; we would all be happy to assist you at any of our individual counseling sessions (dates and time in the Rec Center news each week).