There are medicinal mushroom tinctures that contain a blend of immune-boosting herbs, but they can be pricey. I have never seen any that I consider all that affordable except the individual mushrooms in tincture form from Herb Pharm and other similar companies. There's a good blend from Rawls' Vital Plan, but again, not cheap. Host Defense makes some good blends, too, and can be bought easily online. You can grow them yourself cheaply, I guess, if you're into that.
I use a multi-mushroom spray for immunity from Host Defense. It seems to work well, but I am ridiculously careful about
germs, so who knows?
Lion's mane is used more for nerve health, but there are a lot of others I hear about
for immune support, chiefly reishi and cordyceps, but also chaga, turkey tails, and others.
Glad you are doing well overall!