184, 606 and 202 is supposed to fit about the same but slipper lasts are, as someone already pointed out, a bit special in fit although the 184 is supposed to have been compensated for this.
Do you take a bigger size in 888? Narrower? Wider?
What particular aspect(s) of the fit (e.g. toebox width? toebox height? forefoot width? etc) makes you need the different size for the 888?