Justme15 I would prefer a conventional raft slab siting on bored piers that are at least 3m deep.Conventional raft slabs have edge beams and internal beams dug into the ground and have sand formed slab panels.Waffles sit on the surface and have poly formed slab panels amongst other differences.
Clayton sth in general has moderate to low reactivity soil profiles and some deep sand profiles.There are some localised swamp deposits that have highly reactive clays which are usually dark grey to black you might be on one of them.
One possible reason for your current slab to be cracking is that it doesn't have piers and the nearby large trees are drying the soil under your slab and causing slab settlement.The trees may have been small and not planted when you current slab was built.
If your new slab is on piers then this should mitigate the influence of the trees as long as they are deep enough.