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?

It sounds as if there is movement in the floor. Did the Building Inspector inspect the building work and issue a Completion Certificate for the work? If not there may be structural problems that you should sort out first. The joists could be undersized so the floor is deflecting. I recommend getting in a structural engineer to check this. If there is a problem they will advise what needs to be done. Worth spending a few hundred pounds on this. Rigid floor tiles need a firm stable base which is more difficult to achieve on a timber floor structure. They do not usually work if just laid over a typical chipboard floor. I would recommend employing an experienced bathroom designer who should be able to come up with a design you like and includes the storage you need. They are likely to know tradesman who have carried out successful installations. This may cost more but will dramatically reduce the risk of problems.

Attached floorplan.

I feel your pain............or maybe your husband's. My father was disabled due to the loss of a leg and then a stroke many years later, leaving him paralysed totally on his left side. Thankfully there is a lot more choice nowadays for people with disabilities than there were in his day. Just because you're disabled, shouldn't mean that you can't have stylish bathrooms or mostly what happens....no privacy. Have a look at Living House they have a wonderful range of stylish and practical bathrooms Also:- Premier Bathrooms It might be nice if you have the room, to have a bath and a shower. He might like a nice soak to ease aching muscles and relax!Lastly another site called Bathing Solutions who also have a good range of products. Would love to see some finished pics as it's something away from the normal, and, a little more interesting! Good luck!