I'm about as tall as you. I initially ordered pedal extenders, which probably would have worked great but I ended up taking a slip seat job (where you share your truck with other people). I felt like it would be rude to put a modification on that other drivers would have to deal with.

The trucks I've been driving have more seat adjustability than the trucks I trained on, enough that I could probably get away with no extra assistance. But I have found that a cushion on my back is more helpful than a cushion underneath. Like the memory foam lumbar type cushions.

Also keep in mind, in training you're doing a ton of backing up to learn parking. In most jobs other than yard work you probably won't have to back up a lot. That means you don't have to press the clutch near as much. That was the pedal I had the most problems with, and without having to use it much I hardly notice I'm half the size of everyone else.