I started to say the outfit has a shitton of problems anyway -- starting with the terrible fit on the blouse and jsk, the uncoordinated colours, and nothing else on the outfit actually conveying the effect of sleeping theme. So there's no harm if you want to do an improved version of it.
To be quite frank with you though, the slippers are kinda ugly. Probably a good thing you see them in action here on another girl before you tried it.
If you really want to do a sleeping theme then I'd suggest fuzzy shoes from one of the gyaru or larme brands, and use one of AP's sleeping mask headdress. Gets you much closer to the sleeping theme than wearing actual bedroom slippers. Add a pillowcase bag, then chose between cardi or peignoir (whichever suits your body type more), and the sleeping theme will be even more obvious.