DVI is good, but HDMI is better! It's smaller, leaving room for audio and other things. It's probably already plugged into your monitor too, so no need to find that one DVI cable... it is really handy having a 3.5mm audio out jack too.

The Sophia 2 device is by Atari Age forum member Simius - announcement thread:
https://forums.atariage.com/topic/307...
I believe Lotharek and the Brewing Academy sell them currently.

If you would like a side panel for your Atari 800 you can download the STL files and print your own:
https://www.printables.com/model/7873...

You can find the KiCad project for the circuit board in my GitHub repo:
https://github.com/aeberbach/Sophia2-...

You can also order the circuit board and the side panel from my projects space on PCBWay:
Side panel: https://www.pcbway.com/project/sharep...
Circuit board: https://www.pcbway.com/project/sharep...
If you do they may pay me a small commission.