This

My character is progressing, so it doesn't make sense to have a static alignment.

At first they are likely to be more selfish/self centered due to circumstances, but as they become more aware of the big picture that could easily change in either direction.

Character development doesn't just have to mean bigger stat numbers.

I always thought alignment was silly when applied to non-priest/paladin characters anyway. Who still has the same philosophy at 40 that they had at 20?