Learn how to do auto canceled upairs from ground to platforms. Or platform to top platform. Upair asap and fastfall and there will be no l cancel.
Ive tried practicing lately on upairing marth and sheik to get the flow better. Try throwing up at 0 percent and upair from there. The thing with floaties from what ive noticed is theres no secret besides wicked quick upairs and what you have to do to start that combo. Meaning d tilt, upthrow, or dash attack. But after enough percent combos past the initial starter and one nair or fair is highly limited. Make those upairs sexy.
Ssbm university has a good tutorial on peach combos on fast fallers. At very low percent low bairs and nairs lead into dsmash as well. Then you tech chase into a dash attack. From there you might have another grab, or dash attack. You can djl onto platform to grab or dash attack, or auto cancel upair onto platform, or shark them with upair while floating from under platform, that or simply jump at and nair.
One thing that ive recently discovered is that you dont upair from below on fastfallers falling on platforms at low percents. They can punish that if they get an opening because it doesnt combo and very likely wont cause them to get knockdowned.