Hi @melsky,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
As you would be covering the concrete with floating floorboards, the main purpose of the sealer is to seal the surface to prevent concrete dust; it doesn't need to create any kind of aesthetic finish. Is that correct?
Realistically, you can use any concrete sealer, as long as it binds the surface, which is a concrete sealer's primary purpose. This Bastion Matte Concrete Sealer is a good, low-cost option. You could also use a seal coat of Bondcrete.
To apply these products, you would start by cleaning the surface thoroughly to remove any dirt or loose concrete dust. A wet and dry vacuum is the best tool you can use for this.
Once clean, mix your sealer based on the instructions on the packaging, then apply it using a paint roller on a pole such as this UNi-PRO 230mm Roller On A Pole With 1.55m Extendable Handi-Pole.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
