If your employer coverage is becoming too expensive in premium, deductible and coinsurances, and you considering leaving the employer plan so you can enroll onto one of the Medicare insurance options available to you, you are eligible for a special election period anytime during the year to request enrollment onto Medicare Part A (hospital) and Part B (outpatient services). Whether you currently have only Part A or need both Part A and Part B, there are 2 forms that will need to be completed and submitted in person to Social Security (the administrative arm of Medicare); one form is completed by the employer and the other by you. There is a premium for Part B (outpatient services); the premium is based on the adjusted gross income filed with your IRS tax return. Social Security looks back 2 years to determine what your Part B premium should be for the current year; Part B premiums can change from year to year.
Once you have Part A and B, you can enroll onto a Medicare supplement and Part D stand-alone drug plan /or/ onto a Medicare Advantage/HMO plan (which typically has drug coverage as part of the plan). The Medicare supplement allows you to have freedom of choice regarding providers; with the Medicare Advantage plan you will want to confirm whether your primary care physician takes HMOs and which medical group she/he is aligned with in order to determine which of those HMO plans will meet your prescription drug and medical needs.
Please note that if you are leaving an employer retiree plan, you will not be able to re-enroll once you leave the retire plan.