Back in 2011, I gave myself a retirement pressie of having an en-suite installed in my 1930's terrace house. All water was at the back of the house (kitchen downstairs, bathroom upstairs
My bedroom was in the front of the ho, use. Some years earlier had taken away airing cupboard, between the two main bedrooms, and this area was now stairs up to loft extension (where visiting g.children slept). I worked out that there was just about enough room for a very small en-suite (loo being situated under the slope of those stairs).
It meant bringing water into the centre of the property and I used a local company who had loads of recommendations. I can remember that they needed to check the way the joists of the upstairs ran -fortunately they ran the correct was for them). Small square shower area, tiny wash hand basin, but it worked perfectly. They ran the water and waste underneath the back bedroom floorboards, into the bathroom and then out of that rear wall to join up with the pipework. Was not cheap.....cost me back then in excess of six grand. But it lovely having this, and I would never again be without an en-suite,
You ned to get a really good builder/plumber, one that can properly plan and know what they are doing and you will need to pay for this expertise. Any electrical work needs to be checked and have certification.
It is worth having done if you can afford it. But do not skimp .