In France you go to the Post Office and purchase boxes. They come in various sizes. Last time I did this there as no specific weight limit per box; i.e., you pay a set fee for the box and can cram as much stuff into it as you like. If that has changed, I'm sure someone will correct me. You address the label on the box and hand it to the postal clerk.

In Germany you go to any post office or postal agency and send it via DHL, the parcel service branch of German Mail
Postal agencies can also be found in supermarkets or other businesses, esp. in villages which don't have a fully fledged post office anymore.

You can buy parcels in many sizes there, too.
It does not hurt To bring a few free papers to use them to fill the empty spaces if you don't want to buy this bubble wrap (if that is how you call it)

You can calculate the postage here
http://www.dhl.de/en.html

After much research I too used the post office!It was the best deal and they had the boxes etc available.You may need help filling out the form where you have to declare the contents/value. I pickedup the boxes,took them back to the hotel and then returned to the post office. I took my own strong tape,scissors and some bubble wrap/tissue. There were times when the shop would back it so well that all I needed was the box/tape.I did not let the shops ship stuff back because they charged too much.

Af you are not sending anything huge, the post boxes in France are definitely an excellent option. The employees are super efficient and will put your box together and cram as much stuff as possible into it, with no regard for the official weight limitations. I saw this just the other day when I was roped into being an interpreter for some Korean tourists. I think the cost of the big box (for Korea) was 48 euros.

We are obviously going to the wrong post offices Kerouac!! We have never found their staff efficient