Choose wall-hung fittings wherever possible. It will make your bathroom much easier to clean and give the illusion of space, too. Try to keep walls clear of clutter and consider fitting underfloor heating, so you can keep it toasty without taking up space with wall-hung
If you do plan to change your layout, measure your bathroom carefully. Note the position of doors windows and any pipes. It might help to draw an outline on graph paper, or use an online design tool.