I'm enrolled in GEHA-Standard, plus 1, with no Part B. My wife, the non-Federal annuitant, is enrolled in Part B. Ever since my wife started Part B, in 2016, we've been subject to IRMAA, with pensions and Roth conversions, despite delaying her SS retirement benefits until 2021 (I'm WEP impacted so my modest SS benefits and her spousal benefits from my SS retirement benefits never moved the needle.) We just got our SSA 1099s for 2022 and she paid over $5K in Part B premiums. She had some minor medical issues last year, but we're sure standalone coverage under GEHA standard would have been far cheaper than premiums paid under Part B. She'll always be in IRMAA tier 3, at minimum, going forward, whether filing jointly or singly.
We annually evaluate whether she should dis-enroll in Part B. I'm comfortable with not enrolling in Part B and don't see any current health insurance benefit to have Part B coverage. She enrolled in Part B when first turned eligible for Medicare; and if we were to ever get divorced (unlikely as we've been married for 47 years), she'd lose coverage under my FEHB plan (and I once thought that her FEHB coverage lapsed if I predeceased her -- but OPM clarified that in its literature on survivor FEHB coverage).
I think if you are not subject to IRMAA, Medicare Part B plus BCBS-Basic (or the new FEHB Medicare Advantage Plans standing alone) might be a good deal, if you can stay in BCBS network and are satisfied with the medical providers. My BIL has Part B and BCBS-Basic and the coverage takes care of all his medical needs with debilitating MS and his confinement in an assisted living facility -- we oversee his care and finances -- and he has no out-of-pocket expenses for expensive drug treatments and PT.