There is something called SHIP that will help you. Senior Health Insurance Program. Ours is run by volunteers and is housed in the local hospital. They walk you through the options AND they told me which state and government benefits my parents were eligible for and walked me through the paperwork. They dont sell anything or point you to any company...they explain things. The guy was super helpful to me when we had to relocate my Dad last year.
Basically the way I understand it, each company has different options for supplemental coverage. You decide if you want a deductible or not. All the companies' plans are similar you just pick the company.
Then you need drug coverage. This is where it gets really interesting. You have to pick the coverage based on the best deal for the drugs you are taking.
Advantage plans are located in larger areas or areas with larger senior populations. We dont have them where I live. They are basically like an HMO. You get more benefits in network for a lower price but you give up some options. My Dad was on one in FL. Was great for some things. Really, really bad for others. Overall all, it is a cheaper option but be careful to read about things like nursing home stays. That's where we get burned.