This is the microphone connector CAD
here the Hypophonia Amplification Device
Here the deal
the dimensions are: height 2.5 inches, Length 2.5 inches, and width is 1.6 inches if you include the clip.
for better dimensions detail look into the pdf for the hypophonia amplification device drawing
I base my design off of the sony x11 ultraportable bluetooth speaker
for me this is as small as it gets if you want quality sound and high volume.
The volume control is the + and - signs on the mini-box device. and the P sign is for power.
There is a switch as you request for the microphone connector CAD. this switch will turn off and on the sound.
i also include a stl file so you can 3d print it out to have a better look at it.