We have a very similar story at my org. We run around 100 RDS aurora clusters and switched to graviton. I'm surprised to see 35% gains here, we saw more like 10-15%. But since amazon natively supports mysql on aurora we didn't have to worry about compatibility. Our main highlight was the way we wrote our infra as code where we made switching instances types or service we use fairly simple task, so we have switched instance types a couple of times in past and could easily make dev use t3s. Getting on cloud is a trap and not the usual we deploy on the servers and we live situation. Give weight to write some good code to manage your infra and able to adopt optimizations as they occur. It will ramp up in expense soon otherwise.