For overnight oats we recommend using old-fashioned rolled oats. You could try using steel-cut oats but they might have a slightly chewier texture which means that you'll need to cook them for a couple of minutes the next day (I have not tried this recipe using steel-cut oats though). Instant oats and quick oats are not my favorite to use when it comes to overnight oats because they often result in a mushy texture. If you don't mind a runnier consistency then you could give it a try. Slightly reduce the amount of liquid then.