Not a pro. If I were you (and I have decorated a nursery - this is what I did): Keep your blinds and add curtains. If you agree that dark rooms are best for sleeping, get blackout curtains (and be prepared to pay for them). You will need at least 4 panels for that window, possibly more. Rod supports should extend far enough outside the window that the curtain does not block the window when open (prob min 8", but more is probably better). Put your rod at least midway between the top of window and ceiling. Higher is better. Get 96" curtains. Your decor is all neutrals so I'm not sure why dark blue would be your pick?

I would keep the blinds and add curtains with a subtle pattern/trim to add a little interest.