The first 3 weeks were agony

Yup. Nobody talks about this! You have to break in your legs and build some strength, but it does get better.

anti fatigue mat

Crocs. Stupid-ass looking crocs will absolutely save you when at a standing desk. Or really, standing for a long time on any hard surface like a concrete office floor. The next best thing would be high-end business shoes designed for comfort while you deliver powerpoint all day, or just hiking boots. But crocs are really the most comfortable and are easy to slip off for more appropriate dress shoes if you’re in an office.

Thicker and softer than any standing mat, they freaking deliver. And you can move around without having to be perfectly positioned in a small area. Also, there’s no mat to get in the way of your chair when you sit down.