I solved my issue of not being able to get into BIOS by using the Windows 8 restart to BIOS method and turning off FAST BOOT allowing now F2 and F12 at startup and I'm therefore now ready to install an SSD.
Windows keeps telling me that I'm about to stop receiving updates for it and must get to Windows 10 and having seen all the issues people had with this model going to 8.1 have no intention of ruining a perfectly fine functioning machine in order to try and get updated. Therefore I want to put an SSD in and fresh install Windows 10 to that leaving the existing drive untouched.
I'm looking at mSATA SSD since the price of the HDD Caddy is OUTRAGEOUS and may as well buy a more expensive mSATA since standard SSD + Caddy = $$$ more. However, there seems to be 3 sizes, and the one I was about to purchase comes in 48mm, 60mm and 80mm flavors.
What is the correct size for 772g mSATA?