Correct size SSD for E430

[fredrab]

I would like to install a SSD in my E430.
Crucial's selector allows for either a 9mm or 7mm drive.
Which do I want? Thanks!

BTW, my 3.5 week old E430 began getting a "thermal sensing error" message, and the Lenovo tech said that he recommends getting a replacement, which I had processed just a few minutes ago. When the new one comes in, I plan to swap the drive with a SSD right away.
Any recommendations?
Do I simply make a usb recovery disk of the drive and install the recovery USB on the SSD?