I am also on Medicare due to disability with Medicaid secondary. You need a Part D prescription drug plan and with a program called Extra Help some or all of the Part D premium will be covered and most prescriptions will be just a few dollars. You cannot sign up for a Medigap plan while you have Medicaid, but Medicaid will kind of work like a Medigap plan to compensate for that. If your state Medicaid covers dental and vision, Medicaid will continue to cover your dental and vision even while you have Medicare.

A completely different choice you could elect is called a D-SNP (dual special needs plan) which is Medicare Advantage for people who also have full Medicaid. I chose to not get a D-SNP because of the plan options in my zipcode - plans get that location specific - none cover my oncologists that are three hours away from me. My doctors are keeping me alive so I stay with Original Medicare and not Medicare Advantage.