Keeping feet soft through sandal season?

Every summer the same thing happens. I live in sandals from May onwards, and by June my heels and the sides of my feet feel dry and rough no matter how much I love the freedom of them. My winter feet, hidden away in socks, always seem softer, which feels completely backwards.

Is there a simple routine that keeps feet nice while still wearing open shoes most days? I am not after anything fancy, just something that actually holds up in the heat and the dust. Tips very welcome before my feet turn to sandpaper again like they do every single year.