Combining Shipping

I would like to combine shipping on certain products that can fit multiples in one flat rate box.
I currently offer free shipping on certain larger items, quilts in this case, but for the small items (bibs and accessories) I do charge a flat rate for Priority Mail. I can fit several items in the flat rate box, but I don’t see a way to prevent Woocommerce from charging a separate shipping fee for the second or third item. I would also like to be able to put the small items in with the quilt (within reason) and ship the package flat rate.
I assigned shipping classes to the various items, but I don’t know how to eliminate the multiple shipping charges. Is there a plugin that will do this or is there a setting I don’t know about?
Thanks for your help.

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