Is it better to create a completely separate AWS account or just create a separate IAM user to have a separate development environment?

Question

Currently, I am using these services in AWS:

1. EC2 instance
2. S3 bucket
3. SES for transactional mails

I access S3 and SES services in the backend using an AWS_ACCESS_KEY_ID, and an AWS_SECRET_ACCESS_KEY which basically means I cannot share those keys with the developers.

I would like to create a separate development environment that doesn't give access to those services in production.

I have made some research and I found-out that I can create a whole new account for development environment and then synchronize billing between the two especially that I have AWS credits.

Before investing time in that, I wonder if it's possible to achieve my goal with using a separate IAM identity.