Have a look at the Electro Harmonics PitchFork pedal. To my ears, it sounds quite good down to some 3-4 stops down and 1-1½ stops up.
Alas, one overall problem with most of such things is the tracking speed.
Changing pitch of course involves
tracking, that is, deriving info on the frequency fed into it, and this part could use some improvement.
Else, get a Digitech TSR-24S (low price, much overlooked device) or an Eventide 7000 or higher
EDITED: Forgot that doing fixed pitch change through a song is tricky, as the programmed pitch change of course will change when changing presets