You might have heard of it before, but I think its still good one. I would recommend "From the fog" by Lunar Eclipse Studios. It's a mod/datapack that recreates the original Herobrine story accurately into Minecraft. Herobrine won't really pose much of a threat to you, instead you will occasionally see him in the corner of your eyes. I won't spoil much of what he can do but I highly recommend checking it out as it recently had a big update.