Advice on how to mix a well draining soil that retains moisture for a semi-bog garden

I’ve been helping my dad fix up his pond. He really wants to attract frogs to the garden so I’ve planned a very small bog-type garden to plant alongside the pond. It’s an above ground, pre-formed pond. All the plants like well draining, moist soil. I’m planning to plant the following plants:

Creeping Jenny

Scleranthus Biflorus

Billy Buttons

Dichondra Repens

Viola Banksii

Rain Lily

It’s not a proper bog garden, but I am planning on following a standard bog set up. Based on what I’ve read, I’m supposed to lay a good quality plastic along the bottom of the trench, punch a bunch of holes in that, then add a layer of gravel and sand underneath the soil.

I’ve had creeping jenny and rain lily growing in regular potting mix for around 6 months and they grow quite well as long as I keep their pots sitting in a tray of water. I live in Brisbane, and the area gets a decent amount of sun during the day.

I’ve just dug out a trench that’s about 45cm deep. The soil in the area is an odd mix. Underneath the top 15cm or so of dirt was a big chunk of sand and dirt at one end, and a dense red clay at the other. I’ve bought compost and manure to mix in, but I’m not sure if I need to add perlite, vermiculite or anything else.

I’d appreciate any input anyone could provide. I’m not much of a gardener, so I don’t really know what I’m doing. TIA