secret buttplug: the right size and shape of a pawn from a chess game?

need a base that doesnt taper up slowly, need it to be quick so it doenst slip inside, hmm.
I mighta asked before but I wondered if the anus is less 'reflexive' at night when sleeping - i'd certainly wake up if something was suddenly inserted, but I can definitely fall asleep with something smaller in, but that doesnt do much for me.
I was thinking of an inflatable plug, but one that would inflate very slowly over the whole night, and inflate slower when there's more resistance. that way i could 'work up' to being totally open and relaxed the most possible, maybe to wake up with a really big plug in me

I dont think i've ever seen anything like this on the internet though.