Thanks everyone for the advice.

All-in-all, I've gone for the CO2 route.
I've picked up a nice Aeron BRNO Chameleon Model 4 from the sale section here for a good price. (Budget was a factor)

It doesn't have the small grey bulk-fill bottle, though. So, if anyone has one they don't need or a spare, I would be willing to part with cash for the same as I intend to go for the bulk-fill option. I'm sure the Tau 7 bottle will be identical and others probably. The older ones were 125gr and the latest ones are 150gr.

I'll let you all know my thoughts of the pistol once it arrives.

Kind regards,
Steve