Summary

This is very easy to print with no supports, but it will need the cloud gluing onto the moon (that way you can have two different colour filaments). It's designed to hold this lovely little SPI screen from Waveshare, two buttons that have a 12mm cutout and a 30mm speaker.
https://www.amazon.co.uk/dp/B081Q79X2F

Full details including code on github here https://github.com/SANGERA2/moon-sleep-helper/

This was designed to use an air quality sensor inside the moon, which is why the back is so open and it's separated from the main compartment via a small hole.

The backs have a pretty tight tolerance so they fit on with friction, but you could always add a little glue once you know everything is working.

There is no hole for a power port, my idea was you'd just run the USB cable through one of the slots.

This is designed to be used with a full-size Raspberry Pi so there's a lot of room in there, but it would be easy to shrink down to be slimmer if you're using an Arduino or something. You'll need to use an angled headphone adapter and USB adapter on it for it to fit in.

Buying a KitSound Mini Buddy speaker, ripping it to pieces, removing the battery and powering it via USB is a great option for the speaker and you get an amplifer included! :) https://www.amazon.co.uk/dp/B008YU2P5Q/ Or you could buy the speaker separately and use a cheap PAM8403 amp.

Print with 4 perimeters and 100% infill. Use 0.6mm line width and it will be perfect.