Single Table Design is the way forward here. I can highly recommend The DynamoDB Book [0] and anything (talks, blogs, etc) that Rick Houlihan has put out. In previous discussions the author shared a coupon code ("HACKERNEWS") that will take $20-$50 off the cost depending on the package you buy. It worked earlier this year for me when I bought the book. It was very helpful and I referred back to it a number of times. This github repo [1] is also a wealth of information (maintained by the same guy who wrote the book).
As an added data point I don't really like programming books but bought this since the data out there on Single Table Design was sparse or not well organized, it was worth every penny for me.
[0] https://www.dynamodbbook.com/
[1] https://github.com/alexdebrie/awesome-dynamodb