You can choose between Firestore, Cloud SQL, etc. which can be connected to your Google Sheets using Apps script. However, if you are not familiar with using scripts. I would highly recommend BigQuery as it can directly incorporate your existing Google Sheets, plus it is a pay as you go model.
These are the Google Cloud databases that I could think of that can be beneficial to your use cases of your existing Google Sheets. You can also utilize the 300$ free trial of Google Cloud while finding what’s best fit for your needs. What's great with it is the free tier services that could hugely help you minimize the cost even after your free trial period, especially that some Google Cloud databases are covered with it. E.g. BigQuery which you can be free of use up to TB of querying per month and 10 GB of storage each month.
You can check these public documentation for your references: