Nice house with bags of potential @PickledElectricity (awful for the EA to have included photos - albeit blurred out - of the current inhabitant, though 😮).
We've reconfigured the layout of a couple of old houses - the last one was 400 years old, originally built as an agricultural building, converted to a cottage 200 years later with no indoor facilities. By the time we bought it in 2018 one of the three bedrooms had been kitted out as a large (12' x 9') windowless shower room. Adjacent to this was a disproportionately large landing with window overlooking the 0.5 acre garden.
Previously (from Victorian times till 1990s, I believe) that room and another bedroom were interconnecting, so I guess - apart from the joys of having to traipse outside to the garden for the loo - that layout wouldn't have worked for modern usage.
We toyed with dividing the space to make a smaller - equally windowless - bathroom and third bedroom, but we only needed two, so eventually we just created a hall and landing in order to have the bathroom on the side with the window. We DIYed this work as we've lots of previous building experience.
Currently we're reconfiguring a Georgian cottage that has a horribly inappropriate integral garage (done in the 1960s). We intend to return this to habitable space. We're also in a conservation area, but obviously our decision to remove the ugly street-facing electronic garage door has so far been met with approval.
If you definitely want four beds and can't go into the loft, I like the idea of shaving the back off the largest, dual aspect bedroom to create a new bathroom. Alternatively, swapping the bathroom with smallest bedroom if you could manage with three beds. Downstairs, at the very least I'd want to open the kitchen into the rear of the reception room, whilst closing off the front part to make a separate 'snug' living room.
Although, looking at sold prices for the street on RM, numbers 1 and 2 appear to have extended at the back to increase the kitchen size....