Dogleg, get out of my head!
Those Costco Merino blend socks are amazing value. SmartWool and similar are better quality and feel nicer, but they are quite a bit more expensive.
I used to use polypro liner socks under a thicker sock for high mileage days, but since I started using quality merino blend socks I find I don't have to anymore.
Having a properly breathable boot really, really helps. Waterproof breathable boots are not very breathable at all compared to an unlined boot. I generally only wear them when conditions are "full wet".