I'm lazy and I don't like having to remember "the right way" to run something, so my solution is directories and wrappers. I keep a directory for every environment (dev, stage, prod, etc) for every account I manage.

  env/
      account-a/
                dev/
                stage/
                prod/
      account-b/
                dev/
                stage/
                prod/

I keep config files in each directory. I call a wrapper script, cicd.sh, to run certain commands for me. When I want to deploy to stage in account-b, I just do:

  ~ $ cd env/account-b/stage/
  ~/env/account-b/stage $ cicd.sh deploy
  cicd.sh: Deploying to account-b/stage ...

The script runs ../../../modules/deploy/main.sh and passes in configs from the current directory ("stage") and the previous directory ("account-b"). Those configs are hard-coded with all the correct variables. It's impossible for me to deploy the wrong thing to the wrong place, as long as I'm in the right directory.

I use this model to manage everything (infrastructure, services, builds, etc). This has saved my bacon a couple times; I might have my AWS credentials set up for one account (export AWS_PROFILE=prod) but trying to deploy nonprod, and the deploy immediately fails because the configs had hard-coded values that didn't match my environment.