Courier Specific Packaging Sizes - Royal Mail / Easy Ship etc

Most of our items are sent with Royal Mail which are Letter or Large Letter size. We also send with Evri (via Easy Ship), and they weirdly need us to send our items in larger, heavier packaging so it doesn't fall off their machines! This means that we have to manually amend any Easy Ship order to new packaging sizes, as the product sizes are currently product dependent, not courier dependant.

It would be great if on our products, we could have "if Royal Mail, use X packaging, if Evri use Y packaging" etc, and also including couriers and packaging sizes into the Shipping Methods would be helpful too. For example "If ordered on Amazon AND Easy Ship, change to X Shipping Method AND Y Packaging size", or something along these lines. Also on the Packaging Sizes section in the Settings, it would be good if we could have an option to keep the courier packaging separate, for example Royal Mail packaging sizes do not mix with Easy Ship courier sizing, so they go up in their own courier size and don't mix.