The best option is open enrollment for Medicare or state equivalent and tax funded subsidies for low-income individuals. Unfortunately this option is unattractive to either the left or right
Why is this unattractive to the left? The left wants any change. Obviously universal health care is preferred, but only the right and some centrists wants to restrict the things you mentioned.
On the left I think it is a case of the perfect being the enemy of the good.
One possible explanation for why we got the ACA instead of open Medicare when Democrats had the power under Obama is open Medicare enrollment has a greater chance of preventing Universal single pair down the road.
Open Medicare enrollment is also in some ways close to the status quo of Medicaid.
Lastly, it is a risky option because it pits Medicare directly against private insurance- what if it isn't cheaper or people don't like it
