I Need Some Advice For Someone I Know Who Is Signing Up For Medicare

I know someone who is about to miss his third enrollment period to sign up for Medicare because he doesn’t know where to get impartial - and well informed advice – for which plan he should sign up for.  And more importantly – which carrier he should sign up with.  He has also heard that by not signing up during his first enrollment period, he may have fewer options.  And his main concerns are about being able to go to any doctor he wants, not being denied due to existing conditions and – most importantly – having a provider who will allow him to try multiple strategies to attack a couple problems he has.  Any suggestions on who can answer these questions?