@gmikegreen Once you enroll in any Medicare plan, you are ineligible to make HSA contributions. You may however continue to hold an HSA that was funded prior to your Medicare enrollment and use those funds to pay for your out of pocket medical expenses.
Not only can you pay your Medicare premiums from your existing HSA, to take advantage of having saved that money pre-taxed, you also are allowed a one-time transfer rollover from a traditional IRA account to the HSA account, as a way to "refill" it, if needed. That's limited to once in your lifetime, though.
IRA rollover to HSA (qualified HSA funding distribution) has rules. Keep in mind you must be eligible to make a contribution, i.e. not enrolled in a Medicare program, to do this.
https://www.investopedia.com/transfer-ira-money-to-an-hsa-4770819