After you've chosen an agent, the best way to save on shipping is to remove the shoe boxes and use coupons.
But you can also get more creative, for instance if you buy a blanket and you are just interested in the covers, you can ask the agent to drop the blanket and just send you the cover, this would probably save you 80%, and then you can buy a blanket at home.
In addition to this you can save money by using a budget agent and budget shipping lines, but that comes with the downside of worse service and longer shipping times, respectively.
I strongly suggest using the shipping service that's rated best price to your country, instead of purely looking at the price because some countries and shipping services just don't go together, no matter how compelling it might sound.
Some personal advice, you have to question how much you are actually saving, some people go out of their way to save 1% and wait a few extra weeks, don't forget your time is actually worth something too.
added: 6/26/2023