How to get the cheapest shipping?

I am selling my product on Shopify and TikTok Shop and use USPS ground advantage to ship each order. It costs around $4 a label and it really eats into my margins. I tried using PirateShip and Shipcenter for cheaper rates but it’s not much better. I also looked at USPS stamps but it doesn’t come with any parcel tracking.

Does anyone here know the cheapest possible way to ship super small items online? Or any advice/ tips?