Anymore who gets SSI, automatically qualifies for Medicaid. (except in Illinois or Ohio.) Do you have Medicaid?
If you get MassHealth, then you have Medicaid. MassHealth is the name of Medicaid in Massachusetts. Since you seem to have Medicaid, I don't see why you would need any other kind of health insurance.
MassHealth also runs the CHIP program, which covers kids to age 19. You're too old to get that. So the MassHealth program you are under is Medicaid. If you don't have it, go to your Income Support office and apply for it.