Subfloor construction in a barn conversion

[bmurphy]

I am looking for advice on subfloor construction in a barn conversion which has a few specific requirements.
1) I can't get a concrete lorry anywhere near the property. (3m bridge height restriction)
2) There is an existing solid concrete floor as this is an old stable and I don't want to pull it up, however it is sloping and needs raising between 200mm and 300mm.
3) I need to get a layer of insulation in somehow
4) I want to finish off with a dry screed (75mm) for underfloor heating
5) I also assume all options will require a DPM somewhere in the mix

Any advice would be appreciated ?

Thanks