Going for Original Medicare, with a Medigap plan, the only Plan sort of thing to research is whether to choose Plan G, Plan N, or the HD-version of plans, like Plan G-HD.
Whichever plan type you choose, ALL providers of that plan type must toe the CMS line on how it works. There is no variation.
So after selecting one, then to choose how to implement it. Like using an online broker, if so, which one. If I had to do it all over again, I would have tried SeniorSavingsNetwork, Chris Westfall, in SC, instead of the broker I used, who is touted very often here. I've mentioned why, quite a few times here. The premiums of the same-type plans can be greatly different among insurance companies, but the actual coverage is the same. Don't buy a weasel, even if someone says it's what you need. Buyer beware.
Then there's the Part D drug plan to line up. There, you can go to the Medicare website and look at what is available in your county. For me and some others here, I use a low-premium company, as a placeholder. I am not on any continuing prescription medication. If your DH IS, then need to look through the formularies to see what may be best. The brokers get paid about zilch for helping to select Part D plans, as the premiums are low. I just review mine every open-season, to see if they have made any major changes, like jacking up premiums or whatever. For the last few years I've been with Wellcare, their Value Script Plan. I switched to it from another plan of theirs, that they went up-premium with. I've had a run of antibiotics for surgery this year, those were generic, and no charge to me. An antibiotic ointment was $1.88.
Since we can change Part D drug plans during open enrollment every Oct. 15 - Dec. 7th (I think that's the closing date) for the year starting Jan. 1, if I should suddenly need some really heavy-duty drug help, I'd re-evaluate and switch then. So the period of risk is not too bad.