How do I bathroom / kitchen / extension? etc.

I may have asked this before, but have not got any more decisive in my thinking...

Does anyone have experience of breaking out a concrete floor and replacing it - either with more concrete and insulation under screed, or with raised timber floor?

I have a 1915-ish house, brick walls, raised timber ground floor, which would have originally stepped down into the little kitchen at the back onto presumably quarry tiles on blinding or whatever went under them. It's now level through from the hall to the kitchen, I haven't done any proper investigation but I assume at some point it's been filled in and concreted. It's bloody cold in winter and I suspect is contributing to damp issues.

Does anyone still have a step down kitchen - if so do you have air-bricks/vents from under the raised floor into the lower kitchen? Doesn't it smell damp / you get small beasties in the kitchen? I'm trying to work out how the hallway was supposed to ventilate originally. It doesn't make sense to be a dead corner, and in a terrace you can't go sideways.

I think my options are:

• Leave the floor, add a thin layer of insulation on top so you step up. Easiest to do, won't help with damp.
  
• Break out concrete, dig down a little and replace with new, plus insulation on top, assuming there is already a DPM down there, also not much help with the damp unless there's an obvious gap (eg lapping up to a DPC)
  
• Break out concrete, make new insulated raised timber floor, add underfloor vents to back wall.
  
  

I am also planning to insulate the rest of the ground floor (and some of the walls). Anyone done this? (Themselves or getting people in.)