Sounds like your setup is only 2 steps away from what OP describes:

1. If you need multiple WP instances, you'll need to duplicate that setup with read replica + load balancer

2. If you want to do things enterprise-proper, you'll want to set up a VPC, which means you need the internet gateway + some routing setup

And voila, thats the above architecture. If you don't need it you don't need it. But none of this is particulary complicated to set up if you know what youre doing, especially if you're using Terraform.