I think design has an incredible effect on how large a room appears.
Actually, our shower room is absurdly tiny and dark. When you look at it, it feels spacious, light and glossy. I think this is all down to good design on the part of our brilliant bathroom designer.
So some of the rooms you're looking at may actually be larger than you think.
However, if it helps, our small bathroom is about 1.7m x 2m. The bath is on the left as you go through the door and measures 1.7m. The basin is on your right, and the loo is also on the right, past the basin. Storage space has been cunningly built into the wall, so that shampoos and so on have a niche, and spare towels and loo roles have a hidden cupboard. We had to pick a special narrow towel rail to fit in the space available, but it works.
The layout used to be completely different - the bath was sort of in front of you, with a random useless space beside it where we put the laundry basket, and the loo was on the left and the basin was on the right. Climbing out of the bath, you had to sort of climb past the loo to get dressed. It was probably the worst layout possible.