I'm sorry but what may be appropriate for a 400 pound male of thirty to boost their immune system may be having he total opposite result for a eighty year old woman of 90 pounds.
If there were blanket improvers of such things all would take them.
There are not as all is individual and must be approached as a individual.
Solicite suggestions certainly but be careful to apply them only within this context is my suggestion. Qualified
A holistic practitioner may be most helpful.
"This order considers that progress can be achieved more rapidly during a single month of self-transformation through terrifying conditions in rough terrain and in "the abode of harmful forces" than through meditating for a period of three years in towns and monasteries"....Takpo Tashi Namgyal.