That's pretty much what I did, nice flat ceilings, loft storage and room for insulation:
View attachment 227736
I do wonder if those terracotta walls have any structural strength? I had one between this bedroom and the bathroom next door, it literally fell apart when I stripped the plaster off it so I replaced it with a stud wall, I think because they are so light they don't "settle" over the years like a heavy old brick wall when the joists deflect, they just crack. I also never understood why they built the walls off the floorboards between joists but it's to spread the load between adjacent joists.
How did you connect the new joists to the house at the window side of the room?
When I did it at my house I went from load bearing wall in the middle to an RSJ just in from the windows. At our daughters I could go onto the wall plate direct and that would lower the ceilings by 16cm to 243cm.