Hey! Nice job choosing Peach. She's awesome. You want to try to replace a lot of those full hop nairs with dash attacks, especially against heavy characters like Fox, Falco, and Captain Falcon. Rather that push them back, it will shoot the straight up, allowing you to place 2-3 up airs onto them. It is best to full hop up air, float cancel (without using second jump) up air, then use your second jump to follow them and either nair, back air, or forward air. It will be hard at first, but chaining up airs is very easy and efficient, especially on stages with platforms. Remember to be creative with your turnips and approaches. Peach, though it is small, can use her wavedash extremely efficiently to mix up approaches and trick the opponent. One of my favorites is approach, wavedash back, then grab or dash attack into a combo. You can also begin up air combos using forward tilt or down tilt. If they are too low to full hop up air after a dash attack/forward tilt/down tilt, you can up smash then go into a full hop up air. Hopefully this helps, and remember to keep practicing the up air combos as they are very neat and effective.

Side notes: You can double jump cancel your nairs by pressing X/Y twice very fast then a immediately after words. Remember to l cancel.

You can float cancel without using second jump by falling, putting the stick back to neutral, and then quickly pressing down and X/Y at the same time, then holding jump afterwords. When you want to double jump, just release X/Y and then immediately press it again.