Rather than separate Medigap/Part D, you could buy a Medicare Advantage plan that includes Part D (there are both PPO and HMO plans). The benefits can be richer, the out of pocket is limited, you deal w/ one private payor rather than Medicare directly. The Medicare site has tools to help you compare plans available in your zip code based on your drug list. Then when you get interested in one or more plans, go to their site and they should have a direct comparison for what they offer vs. traditional Medicare, including applicable copays and OOP limits. You can also see provider directories and the full Evidence of Coverage that lists out all benefits.