When I retrofitted my wiring I often found the easiest route was not the most obvious or direct one. I also tried to maximise the use of existing corridors (the void between the downstairs ceiling and upstairs floor, and into the attic space.
You might find you have access via boxed-in soil pipes, behind bath access panels etc. Biting the bullet and making a mess in some locations could then make it easier to run cables to multiple other locations.
Just one example from my cabling - to get to the boiler area would've meant lifting the floor in the bedroom and ensuite, and all across the landing. In the end, I could run under the upstairs ensuite floor to the top of the downstairs boiler from the soil pipe. I then continued up the boxed-in soil pipe into the attic and across the loft space to where I needed to end up.
HTH,
Tim.