Hi Chris The cheapest option is Grind & Seal, but we usually recommend Mechanically Polished Concrete for inside of a home. This is by far a better option, if you were to go for a Matte or Satin finish it is less expensive than a higher gloss finish. Mechanically Polished Concrete does not have a top coat sealer requiring drying and curing time and does not need re-applying in the future which will save time and money in the long run. Because Polished Concrete does not require drying or curing time it can be used as soon as the process is completed unlike the Grind & Seal option. All floors are slippery when wet, a non slip agent can be added to a top coat sealer which would be the Grind & Seal method which we do apply in a shower area if there is not a shower base. Polished Concrete in Matte and Satin finish does have a very good slip rating, has no grout lines as with tiled floors where dust can get trapped therefore it is a wonderful easy to clean flooring solution. Hope this helps, I have provided some details regarding the 2 main processes below There are 2 different finishing processes / methods that are commonly called Polished Concrete, they are very different so it is important that you know the difference & which process/method you want and which is being used on your concrete Polished Concrete - 12 to 17+ step process During this process the concrete is ground to the desired level of stone exposure. After grinding the concrete surface, the Polished Concrete process begins. This process has a densifier applied in multiple stages that is absorbed into the concrete which hardens and strengthens the concrete. A Polished Concrete Floor is Polished in Multiple stages in a Refining Process using diamond tooling & resin pads. A penetrating sealer is applied in the final buffing stage to complete the process The "Polished Concrete" process has "NO TOP COAT SEALER" applied therefore there is no drying or curing time required so your space can be used as soon as the process is completed Grind & Seal (a 3 to 4 step process) This is NOT Polished Concrete. Grind & Seal is often referred to as Polished Concrete, this is the cheaper substitute that gives a "Polished Concrete Look" With the Grind & Seal method the concrete is ground to the desired level of stone exposure and a TOP Coat Sealer is applied such as water based, solvent based, urethane, acrylic or epoxy requiring 5-7 days to dry & cure

Having experienced a leaking shower, a step down sounds like a welcome added precaution, which seems rarely done. Supposedly if there is no hob or atepdown there is an angle, and obviously the whole thing is supposed to slope towards the drain anyway, but BeachBathrooms' earlier comment about capillary action rings true. It became obvious very quickly in our other shower that water was creeping across the grout outside the shower so whatever was meant to be done either wasn't or wasn't correctly done. Then there's the modern hotel bathrooms I've experienced where the water simply splashes out too easily. All in the name of style.

Love it as is. Well done. The void above living will let on light, just be careful of not letting in the western light too much. So some way to shade house on the backyard end. would be good.

electric underfloor heating is great for bathrooms (and laundry, mudrooms, entry and hallways when it needs to be left on for weeks at a time and not much good for a ten minute shower) and is preferable to anything visible like hydronic heaters that take up wall space but your voids will suck most of the heat upstairs ..our reverse cycle AC has been much more economical to run than the whole floor electric slab heating that we had in our previous house (supplemented with a wood burner and gas log fire in our cold climate) but we made sure that the void over the stairs was able to be blocked off to zone heat downstairs with separate heating upstairs but having lived in different areas of Sydney i'm wondering why a new built well designed house with great insulation would need more than modest supplementary heating that can be more economically provided with AC