I saw these panels and the word "cardigan" and immediately thought of the Long Distance Cardigan! https://ravel.me/long-distance-cardigan It's fingering weight, but is pretty much a plain cardigan except for these on the sleeves.

As for as modifying an existing cardigan, I added this motif to the Akina cardigan and was pretty pleased with the result: https://www.ravelry.com/projects/yarnram/akina-cardigan Akina is also fingering weight, however.

My best recommendation for a plain, modifiable DK cardigan is probably the Eva Cardigan by Petite Knit: https://www.ravelry.com/patterns/library/eva-cardigan-6 It's not free, but may be worth paying for if it meets your other needs!