Is there any way to conditionally assign package type to calculate accurate shipping costs?

[HolleyGirl]

Shopify calculates my customer's international shipping costs at checkout based on the default package type.  This results in inaccurate (too low) shipping fees for my customers whose shipping label cost uses dim shipping calculations.  Is there any way to calculate my customer's shipping costs based on a default package size that is determined at checkout by rules I set up (i.e. total order volume, number of items in an order, items from a specific collection) ???  This is something included in many other platforms but appears to be missing from Shopify.  I would even be ok with a reasonably priced app that isn't too complicated.  I've looked into Boxify and several others but they don't seem to solve the problem in the way I indicate above and have a lot of things I don't need.  For reference I have over 2000 separate SKUs all with different dimensions.  I use 6 different Boxes and 4 separate poly mailers.  I want Shopify or an App (if absolutely necessary) to change which Package size is provided the carrier in it's shipping cost calculation based on order volume.  Any advice?