We've just had ours done - it came to about £9k in the end and was finished on Christmas Eve, thank goodness
It's a small room (3x1.5m) but it was completely covered in horrible tiles, so we had to include replastering and some remedial brickwork (missing lintels) and joinery (skirting, window architrave).
We went to a local bathroom supplier recommended by our plumber. They talked us through all the choices and permutations.
We put in a bath with a pumped gravity-fed digital shower over, with loo and basin in fitted unit, Karndean flooring (smart and hard-wearing but warm under foot).
The fitted unit pushed the cost up a little, but was the best use of space because the end wall is only 1.5m wide. It gives us a nice long countertop and a neat finish.
Get a good shower - recommend Aqualisa. We have a diverter fitted, so one button runs the shower, and another pumps water into the bath (no taps!).
No tiles either - we fitted shower panels (also known as wet wall or mermaid panels). No grout!
Those towel rail radiators look nice, but don't heat the room enough, especially the chrome ones - we went with a traditional radiator and towel racks.
Fit a good extractor fan to reduce mould.