I'd recommend sticking with relational databases since they all support JSON columns now. If you need horizontal scalability then there are many choices like CockroachDB, Yugabyte, TiDB, Vitesse, MemSQL, and others.
If still want a document-store then RavenDB is a great choice with proper clustering, full-text search, SQL-like querying, graph queries, etc. ArangoDB is also good choice.