Migrating from Firestore to CouchDB

We are using Firebase cloud functions, cloud tasks, Firestore for database currently in our project.

We see many limitations down the line when it comes to firestore. As our's is a write sensitive application (Score submissions from users for leaderboards), we reach the limitations of firestore pretty quickly.

After lot of research found CouchDB as one alternative. But have following queries 1. How can I assure the couchDB instance is always available when requested from any cloud function instance. 2. What could be the cost comparison with Firestore? 3. Will the migration be smooth? Or any limitations I need to be aware.

Can someone suggest their view on this?