[Q] Low Level Formatting galaxy s2

Hi,

I want to sell my galaxy s2 but want to make sure that the buyer can not access any of my previous pictures or chat logs.
I have formatted the partition in Windows Explorer which pops up after hooking my phone up to my desktop, but I can still read the sectors using GetDataBack for example.

I think low level formatting is the solution for this, but before I try this, I want to make sure that nothing of the vital stuff (bootloader, recovery?) gets formatted also and I am left with an unusable phone.

I just tried to flash my device using Odin without putting my S2 in download mode but this doesn't work. I tried this, because I think that I can't also power my device on and put it in download mode after a low level format.

Is this true? What is the right procedure to make sure all of my data is gone and I am still able to set my phone to default firmware so I can sell it?

Many thank in advance for your expertise.

Kind regards,

Funxx