You should use the TRADA tables (joist deflection limits) to calculate whether you can come off the leading joist of the mezzanine and span to the facing wall without any other vertical support (pillar) or a more substantial member like steel beam.
Attaching to the facing wall can be done simply enough with a wall plate and some appropriate anchor bolts at specified centres.
My approach to such things would usually entail speaking to builder mates in the pub and doing tons of research online and reference to the trada tables and if it looked like it all didnt seem to be really easy and well within an 8x2 @ 400mm joist limits get an engineer in. But that's me, on my house, not advice.
EDIT: Whats the span of the leading joist of the mezzanine? ANd what are the joist dimensions?