Look at the Design Pattern: Associated Items for a full description for how to access these other Items by name.
This should work with your naming scheme. You just need code like this:
val nameParts = triggeringItem.name.split("_")
val humidityName = nameParts.get(0) +"_Humidity_"+nameParts.get(2)
Then follow one of the techniques in the DP to access the item.
as long as you as you split the parts of the name consistently it doesn’t matter what order the parts of the name are.