Creating provisioned postgreSQL cluster

I currently have a solution in production which is using a serverless v1 postgreSQL cluster. At the beginning it worked well as the workload was quite spiky, but now with serious customer growth the database is running at 64 units pretty much all day long and already running at 128 units at times. We are running out of growth capacity so really need to transition away from serverless into the provisioned capacity.

From the AWS console I could create a multi-AZ cluster using postgreSQL 13.7-R1 which will create me 3 ec2 instances each in different availability zones. Is it possible to create this via my serverless.yml file as I can’t find any examples of this, only single db instances.

Alternatively I may be better using the AWS Aurora DB Cluster which supports up to 15 read only replicas. Is this configurable via a serverless.yml file?

If this is not the best approach, please suggest alternatives.