Mike Wye (the Lime specialist) have a good guide but we found that availability and cost of materials was a problem, as was the definite mix ratio, so here's how we did it.
Dig out the solid earth floor. If you have shallow foundations, come in from the walls at 45-degrees, so you don't undermine the structure.
Roughly flatten the earth and remove any sharp edges or prominent sharp stones.
Cover the earth in a geotextile membrane which stretches up the walls to the level you want the finished floor.
Fill the room with an expanded glass aggregate - GlaPor or PorAver (same thing, different sources). To a depth of at least 10cm. This stops any moisture wicking up and in to the materials above.
Use a compression plate/wacker plate to compress the glass aggregate down. It will shrink by one third of its height. It's VERY dusty, and an irritant, so wear a mask and gloves.
Cover the glass with another layer of geotextile membrane. This stops your finer-grade insulation from falling down between the glass blocks and helps with laying the next layer.
Mix up a quantity of insulated limecrete: 1 part NHL5, 1 part Sharp Sand, 2 Parts LECA clay aggregate.
In practice, that's 1 bag of lime, 1 bag of sand and 1 bag of LECA. You may have to make it in halves depending on the size of your cement mixer. You will need something like 6-8L of water, and the finished consistency should be just sticky enough to adhere to a rubber glove, but it should ball up.
Leave to set for 7-14 days without walking on it.
Mix up a 'screed' (top, finer layer) of 2 parts Sharp Sand, 1 part Building Sand and 1 part NHL5 with enough water to make it turn to something like Houmous. Add the water slowly - it doesn't take much to turn it from a dry, clumpy mix to a wet gloop. Literally a cup full will make a big difference, but it takes a few minutes for that difference to show. Mix for at least 20 minutes and then let it sit for 10-20 minutes before you spread it on the floor with a trowel.
We bedded Indian Stone flagstones directly in to this lime screed layer. If you do that, make sure you soak the stones well before you lay them, or they will suck the water out of the limecrete and it will set too quickly.
If the weather is warm, consider wetting or misting the limecrete and stones for a day or two, every few hours when it's warm.
Leave it for at least a couple of weeks before you walk on it.
We found that both Ty Mawr and Mike Wye were good sources for information. We sourced the LECA from Jewson, the GlaPor from Ty Mawr.