Can someone tell me if there are DRM free physical copies that can be bought?

No. Currently all retail releases are Steam. There was a DRM free DVD available to kickstarter backers who specifically requested it, but that was a limited production run exclusive to the kickstarter.

gog.com has Divinity Original Sin, for download. DRM free no need for a steam account needed or internet connection to play it unlike Steam. The Amazon.com has it too, they will send you the DVD, but you still will need Steam to play it.

Yes, you can simply copy the Gog retail installer files to a DVD(s) and file them away for backup/storage. If you need to re-install the game, though, it'd be faster to simply copy the files to a folder on your hard drive and run setup.exe and install from there--the install will run much faster that way. (With the Gog version the DVD does not have to be in the drive, btw.) Current Gog install version is up-to-date, so you won't need any patches until Larian releases the next one.

I highly recommend you use a Read/Writable DVD so that you can add new patches as they come available or delete older install files and replace them with newer ones as the newer versions of the game become available.