Mains, PSUs and other goodies.

[Rogue]

Yes in theory, but you'll need to support the joist at the wall at each end using joist hangers and not just terminate it at the wall. Although just having an additional joist on the floorboard will improve the 'bending' aspect by spreading the load, it wont reduce (indeed it will increase) the shear force at the wall and the underlying joist could still fail with the load.

Which realistically means "no" in this scenario. Fair enough.

The correct solution...

...sounds painfully expensive and simply not possible at this moment in time, certainly. Hmm.

Incidentally the minimum joist size now acceptable for loft conversions and new builds is 9 x 2 but 10 x 2 is usual as this matches the 10"/250mm insulation depth requirement and allows direct boarding over.

I think the first step will to be to work out the joist size and then plan around that in terms of what can be safely done. That might scupper things more than anything else.