Like you, I'm also on my feet all day, so I really do sympathise.
About 5 years ago I discovered Flyflot sandals and shoes, and they are without a doubt the most comfortable shoes I've ever worn. They can be a wee bit pricey, but no too bad, but they last for ages so well worth it.
Their secret is that they mould themselves to fit your feet perfectly.
They have their own website, and you can buy them on Ebay and Amazon as well as a lot of the usual shoeshops.