What's the distance between window, and the wall behind the sink? If its big enough, you could possible create a rectangular glass enclosure for the shower where the sink is, up to the window, removing the stud wall and replacing with glass. Put the toilet where the shower is and but the sink on the wall at the bottom. Without knowing the distances of all walls, it would be hard to say. There's a good chance that won't actually fit! Failing that, replace the stud with glass, some fresh tiles and shower. Perhaps a dark wood floating cabinet, with under lightings and a bowl sink on top, and a full wall mirror on the wall?

Attached floorplan.

Hello Karen, Yes a wet room style, there is no need for a glass partition at all (although some people do like to add one anyway) and in a large space can be nice. In your case there's no need and therefore no need to have a specific shaped tray.. The room is fully tanked and therefore the shower spray will go directly towards the floor. As you can have a wall or ceiling mounted shower rose angled where you want and the floor will have drainage usually a gradient but there are several options here. The "tray" often used will be hidden under the tiling or finish of the flooring and so specific shape negated.. For a seamless look I like floor and walls to match.. Of course how you want to deal with that is of course your preference.. It does though give you far more scope with the room, because you do not need to angle things to make them fit.. I always suggest wet rooms specifically for the reasons I mentioned and have been using this term for a long time which for me works to describe what I'm suggesting. I think it will work for you nicely.. You could also consider built in towel shelving and I rather like the seat in the second image.. some visual inspiration. : ))

Our guest en-suite is pretty much the same size as your loo 2.60m x 1.40m. It was built as a wet room with underfloor heating, but we added shower doors after a while, as the toilet (seat) would take a long time to dry after showering. I love the layout, it's simple and efficient. As for colours, my preference was for black tiles on the floor and red glazed tiles in the shower to complement, however hubby thought it would look too Gothic and we ended up with some safe 'swimming pool' glass mosaic. There's also a slim towel warmer behind the door, not visible in the photo. As your space is wider, I think you could create an alcove like in the Grosvenor Riverside pic. Let me know if you want more details, I can give you exact measurements if you need them. Good luck!