Onesies are helpful to keep waistbands hidden and reduce noise, as they cover it and stay tucked into trousers/skirts but then you have to think about having them out to dry after washing, if that is not possible look into buying leotards or similar bodysuits that don't have snaps in the crotch.
Loose baggier trousers are always good or if you prefer to wear them then long (below knee) length skirts. Tighter clothing tends to create an outline or bulge where the nappy is. Tights or leggings can also be good if worn under other trousers or skirts to prevent bulkiness and outlines and reduce noise.
Long tops that come well below the waistline will help cover anything.
Clothing made with noisier fabrics (think like tracksuits) can help cover noise if anyone does notice a crinkle or rustle they'll just think it's the clothes.
Wear clothing that draws the eyes upwards, brighter colours, patterns etc. on a top will help keep peoples eyes higher than your waist, conversely very plain trousers with no bright colours or patterning above the knee to draw attention away from that area.
And finally (and probably least helpful) is Confidence. Just make sure you move around with confidence and don't think about your nappy and how much noise it's making or how big it is. If you are creeping around or trying to move in a way that hides your padded rump then people will notice more and wonder why even if they don't notice any nappy, it will draw attention to you.
