All the chemo your policy or contract spells out.
Don't you believe in private contracts?
It's like anything else you buy. You contract with one of those food delivery services, you pay a monthly or annual fee to have a certain number of steaks, so many blocks of cheese, so many hams etc. delivered to your home over the course of a year. If you want more than what you order, you buy that separately.
Same with healthcare. If I want just a reasonably priced catastrophic policy that will take care of the really big stuff I can't afford, I should have the right to buy any such policy that is available. (In the case of the OP such policies are not universally available.)
Or if the federal government simply put together a catastrophic insurance pool at a reasonable rate for everybody, that alone would bring down private insurance premiums down to an affordable level for just about everybody. Then pass a law that everybody will be required to provide insurance OR pay the costs of their healthcare to the best of their ability and that brings costs down even further because so few charity cases will involved.
There are all kinds of ways to address the system without the federal government taking over control of all.