Do you have a wideband? What do you see for a/f? Are you running too rich? I'm asking since otherwise, how do you know you need tuning with a piggyback or full EMS (standalone)? Or maybe you're just planning ahead?
A piggyback is an add-on that runs with the stock ECU or in your case with the Blitz modified stock ECU. The piggyback typically controls fuel. For example adding an SAFC piggyback will give you fuel control (usually only above ~4000 rpm since the stock ECU has tight control below that); another piggyback is the MAPECU which does two things, it converts the stock MAF air metering to a MAP system (like the old school VPC) and it also controls fuel. Some piggybacks like the MAPECU2 also have some timing control but not as complete as a full EMS (engine management system). Examples of full EMS (which usually completely replace the stock ECU) are AEM, ProEFI, Motec, Haltech, HKS Fcon Vpro, etc.
If you can't tune timing then you are limited as to how much boost you can safely run with the stock ECU's timing which is aggressive; if you can pull timing with proper tuning, it usually allows you to run more boost, get more power but that has to be done by a knowledgeable tuner since there's a point of diminishing returns.
IMO, for stock twins and even small singles you can do very well with just a piggyback and a decently retuned stock ECU with the kind of features your Blitz has, or like a gForce ECU is another modified stock ECU that was widely used in the past. When you start getting into larger turbos and/or looking for optimized tuning, a full EMS/standalone is a much more powerful tuning tool.