DIY a new subffloor from a loungeroom

Hi all,

Hello all,

My very old 2 bedder doublebrick house has a few problems, so given the cost of getting the profesionals I have decided to continue do as much as I can.

My issue at the moment is the loungroom floor & subfloor is in dire need of repair/replacement. It is uneven and walking near an exit door makes vibrations and is bouncy.

The room is roughly 4x6 metres, with an old hybrid floor ontop of the orginal hardwood floorboards. The main problem is the floor is very uneven with I assume rotten beams/bearers and I assume also the stumps, although using the keyhole camera they look OK. So my plan is to remove the old floor and while im at it, the old non functioning gas heater in the fire place and put in a new sub/floor

So under the floor is around 55cm of air and then the dirt ground.

I want to pour concret in 12 places to make a soldid foundation and use steel stumps bolted onto the concrete with boxspan/spantec beams to create the subfloor, spoken to council and no permits are required as its not load bearing, my question is which is the best place to purchase the pier, pier heads ( adjustable ) , steal beams ?

live in Melbourne, bunnings has a few products but not all.
Also any tips most welcome while im in the planning stage.