As noted above training, sleep, and nutrition in the right balance are key.
With that in mind what you are really going to want to look into (based on wanting modulation and balance) some adaptogens.
Reishi (what you listed) is definitely a good option. Many other mushrooms take a varying role in benefiting this as well (with Reishi probably being one of the top in just immunity regards), but look into Cordyceps, Turkey Tail, and various others and determine if they seem to fit your circumstance.
Outside that I personally like Eleutherococcus Senticosus/Siberian Ginseng for this purpose.
Panax Ginseng and Atragalus Root may be worth looking into as well.
Again hopefully that gets you started, I’d be glad to help more, but with adaptogens it also kind of depends on what you are looking to adapt against!