The Question is, does OWC ship to Germany. I mean if I have to pay even more than these twice as expensive SSDs, then I guess I have to look for a different solution for my PowerBook
You may get OWC IDE-SSD-drives at "amazing" but they are more expensive than the mSATA-converter solution and they will get "warm" too.
As I've said - I'm running an OWC-SSD-IDE-drive in a 12" iBookG4 which gets warm, but there's no temperature-monitoring for the drive.
An I have that mentioned mSATA-converter solution in my 12" Powerbook, which has the same specs as yours.
With the mSATA the fan were continuously humming... I've got the advice to replace thermal paste and pads, but that didn't solve the problem. Then I found "G4FanControl" and after setting the temp-threshold for the drive to 60-65°C the problem was solved. It may get a little red hot steambook sometimes, when I run TFF, WebKit, VirtualPC7 and other stuff together, but it's the best wrist-warmer ever and I wish I had one like that in my times as a student, when room temperature was about 16°C in cold winter-days

So no regrets on my side about mSATA-converter upgrade and speed is great.
There had been some discussion about bad ways of 5V to 3V voltage reduction. The above mentioned Delock converter offers the best of all options for that purpose. Just browse the forum. There has been a lot of talk about mSATA, converters and temperature-problems ...