Kudos to the hiking boot manufacturers! I so do wish I could get new soles in the way I could 20 years ago. I used to get through two or three soles before the uppers wore out.

Cotton makes very good sense. It has a high environmental impact when made, but if you've no plans to buy more for a long time, then it's the best stuff to wear. It's cooler (as I'm sure you know already), needs washing less often because it breathes better, and doesn't release plastic microfibres when washed.

Uniform is tough. My best suggestion is occasionally dying stuff, but I don't know what the environmental costs of different dyes are.