floor slab mix / reinforcement

If you don't tell us what you intend to put (or build) on this slab, how can anyone possibly tell you what you need?

It's a floor, hence the subject title of 'floor slab', coupled with the opening line: 'I'm now ready to pour my floor slab.'

HTH

My guess is either a bathroom or a kitchen, possibly a bedroom, so the heaviest thing it's likely to hold up is a washing machine.

To the OP, no you don't need reinforcement, nor fibrin. When you ring to ask for premixed, they will ask you what it's for and deliver the correct mix, or if you decide to mix it yourself, a standard

Oh sorry, its easy to forget not everyone else knows what you are up to !! Its the floor slab of the extension I am building. Slab on top of 75mm kingspan, with 25mm kingspan up the sides. Thanks, Simon.

You shouldn't have to guess, which was my point.

No need for mesh reinforcement as it isn't loadbearing. Adding fibres might help to distribute future shrinkage of the slab into a myriad of tiny harmless cracks rather than a small number of wider ones, but they are not essential.

If you tell the readymix company what the concrete is for, they will recommend a mix, or a choice of mixes. They will also offer admixtures that help make compacting and finishing easier.