I only have Part A, so I did search for the answer. The answer is that you only need part A.
I think it's AMAC, the alternative-conservative retirees organization, that had an answer to that question.
About Part B. A lot of people think that they have to have it and pay that monthly premium. But not so. The way it's done is a retiree has to opt in to part D but opt out of part B.
It does seem odd that Part A alone would suffice, i.e., no physician or drug coverage.
A "crappy plan" in the Obama terminology.
I called Social Security about that( Dropping the monthly $105 or whatever) and I asked specifically if it could be re-instated, and I was told that I could drop it, but there was an increasing penalty to reinstating it, at an exorbitant rate. The $105(+/-) would increase 10% per month for each year it had been dropped.