How many boxes of stuff do you have?
I used International FedEx, but only shipped about 16 legal file sized cartons from the US to Paris. 10 years ago, that cost a whopping 2,000 USD, but it all got here safely.
If you go through La Poste, you'll have to identify all the contents of each box, weigh each item, add the value and total all that up on a Customs Declarations Form.
You can check the restrictions on box size on the La Poste website, as well as price options.
If I were you, and didn't have too many boxes - and especially if they were heavy, i'd use either DHL International or International FedEx - just because there aren't as many restrictions to size and weight.
I recently downsized apartments, and shipped a lot of furniture and other stuff back to the US.
I used Grospiron International and though you do have to fill out a lot of forms, it was the most affordable and dependable option for me. I only spent 2,500 EU for a whole houseful of stuff.