Can I do what I want? Is there a good book? Is is diy or do I need
an expert?

It looks possible to me, but you need to get a structural engineer to
calculate it. In particular, the joists may currently be used to reduce
spreading loads from the roof. It must be ensured that the new joist
position with less leverage is still sufficient for that purpose. Even if
not, there's probably a way through, such as using hidden metal rods or
flitch beams or something.

As to whether the work is DIYable, that depends on your experience.
Personally, I'd get a builder in to do the structural stuff, but would
probably put up the plasterboard, insulation and electrics myself. (I'd get
a plasterer in to skim it).

Christian.