Rike, I order my batting at quiltmania.de. I like the unbleached cotton batting they have there and it's less expensive than elsewhere. There are other online quiltstores in Germany where I look for sales every now and then like quiltecke, quiltfun or Sue's Quilt Shop.

If you don't mind having a thicker and firmer polyester batting you could also take a look at the 'Holland Stoffmarkt' that tours throughout Germany (just google it). I guess they may also have cotton batting but I 'm not sure. Most likely they also come near where you live. It's a good source for fabrics of any kind and supplies too. Less expensive than in the fabric stores.

When you visit the US I would suggest to go to a quilt store and look there for fabrics too. You are going to feel like a kid in the candy store. LOL And get some basic rulers like a 12.5 inch square ruler.

For ordering fabrics I would also recommend fabric.com. I order there all the time besides from MSQC and I love them. Don't forget that you are allowed to import goods for approximately 430 Euros without paying customs duty.
If I can help you with anything else just send me a pm.