Find a place in the city that specializes in orthopedic inserts and have them watch you walk and see your worn shoes & boots.  They'll get the correct inserts instead of wasting effort and money trying them on your own.

Been there and wish I had done it earlier.  They're spendy but after a year or better I can wear shoes without them.  Still need them in my boots.  I don't walk with pain in the mornings like I use to.