Precision M4800 DVD Bay caddy for additional drive

Hi, I have a new M4800 with 256GB mSata SSD and 1TB Sata drives. I want to add another 500GB+ SSD drive which Dell say is supported using the DVD bay. I know I need a caddy but am unsure what size to get. The DVD is identified in Windows as :- HL-DT-ST DVD+-RW GS40N and is a slot which externally looks approx 9.5mm but am not really sure. Can someone advise to a suitable caddy and also if it would be better to use the caddy for the 1TB mechanical drive and the built-in slot for the new SSD. Also any SSD suggestions would be much appreciated . Thank,