Cosmos DB is a document based database, which is a great asset especially for high-performance, high-availability solutions. If you have not done so, you should try out multi-master mode. It is a reliable solution to get rid of synchronization headaches by clicking a check mark to sync data between Azure regions.
There are interesting features now newly available for Cosmos as Scott Hanselmann and Kirill Gavrylyuk show in this Azure Friday episode.

A new free tier is introduced, an automatic scaling feature called Autopilot
and a 33% discount for multi-master accounts are announced, as well (https://azure.microsoft.com/en-us/updates/cosmos-db-multi-master-promo/).
The first two features are in pre-view, while the discount is valid right away.
Important to know is that existing Cosmos DB accounts cannot yet be used to leverage the new features, due to the fact that the new stuff is limited to new accounts, yet.
Obviously, this is going to change with GA. Autopilot RU cost rates are also a bit higher than normal ones, but you still should be able to be better off looking at the weekly or monthly average , if your application’s DB usage is not constantly spiking.