How do I stop/prevent heel blisters?

My shoes definitely fit properly. I get blisters on my heels all the time. Where I live it's very hot and I play for a long time, so my feet get really sweaty. What are the best socks I can use to prevent heel blisters? I currently wear Copa 17.2s and they fight snugly and are comfortable. They are tight on my heel when I first start playing but I get blisters when my feet sweat a lot.

All advice is appreciated!

These heel blisters are really holding me back. I want to play and practice more but its hard with the constant heel injuries.