You mention “I have checked our electricity bills and it seems quite different to a normal household bill.”. That would suggest you have a Smart Meter and have a detailed understanding of your electricity usage and behaviours. That will help in assessing potential suppliers. If not, I would suggest you organise a Smart Meter for your lot. In NSW at least, there should not be a charge for that. Then work out your patterns.
Armed with that information, then assess the options. And there are LOTS of options. The comparison sites can be helpful, but they can also be a somewhat blunt tool. Some brokers or consultants connect with your Smart Meter, analyse your data, and provide recommendations. That may be a good option for you, especially if your bills are high – the savings will pay back the cost quickly.
If you’re also looking at the common area electricity via your EC &/or strata manager, in a building of that size, a broker may also add value quickly. Bring the broker in at the same time to do multiple lots, and you may make some savings on the broker costs too.