You seem to be missing the very real practical point that the majority of people below the age of Medicare eligibility have health care provided by their employer. While there may well be a hypothetical system-wide saving to offset the increased taxes you propose, the average working person sees only higher taxes. This cuts across all classes of workers. The union leaders who negotiated healthcare benefits will see it as at attack on the labor movement. HR departments will see this as diminishing the package of employee benefits provided by the company. So you need to think of how to get from where we are to where you want to go.
Maybe you could first focus on having government provide age- differentiated group rate, subsidized insurance for all comers. The government program would function like an insurer in paying claims. This could be accomplished by extending Medicare, but if not accompanied with adequate funding, it would be viewed with suspicion by the elderly as an attack on the solvency of their healthcare financing system.
Taxes to fund such a system need to be broad-based and include more than just those who need their own insurance. That was a pivotal failure in the structure of Obamacare. It led to the massively regressive and unpopular individual mandate. Taxes collected for healthcare need to be maintained in segregated accounts by law, so they can’t be used to cover any other priorities. Otherwise people will rightly view it as a blatant rip-off.
Scandinavia has interesting approaches that should be evaluated. But they have a different history and a different set of problems. Approaches that work there may not work here.