Don't forget that his wife is also a US Senator, so he is covered by Uncle Sam regardless of whether it is by virtue of his former prez status or his marriage (or whatever you wish to call it) to Hillary.
For the record, I think Uncle Sam should supply health insurance to former Presidents.
Former presidents, like members of congress (once vested), are covered by the same healthcare plan that was extant while in office. And it is proper that such be the case.
He is most likely covered by Hillary's plan... or the cost will be a gift from an unstated contributor - possibly one in yellow robes, etc.