App for small parcel rates

[Remoov_Main]

Hi All,

What app would you recommend to integrate with our Shopify store so that customers can get parcel (USPS, UPS) shipping rates at the time of checkout, pay for the shipping and for us to print the labels.  We have the item dimensions so we would like to automatically add a certain number of inches in each direction to estimate the size of the package. Any recs?

Thanks!