Rules:
*You can teleport into and out of it at will
*It has a couple of plug sockets and can connect to internet from the region you teleported in from
*You can take objects and people with you
*As already stated, it is 3m^3. The walls are plain plaster with a light in the middle of the ceiling. The pocket dimension is topologically toroidal, so if there weren’t walls and a ceiling/floor (which you can actually destroy) you would loop if you went more than 3m in any direction. Gravity, then, is artificial and can be altered to anywhere from 0 to 2g from a dial on the wall.
It sounds really boring but… Reading nook - just a little spot to relax and read. Kit out the floor with pillows, the walls with shelves, and paint the ceiling to look like the sky.
Getting to experience improved mental health thanks to having a private quiet place you can think and relax? What a weirdo… (That sounds amazing, I’ll take two!)
I’d put a little fountain in the corner.