On the plan Homesundertheammer has produced has wasted space by the door. I think the shower and the bath together like that are virtually unworkable as far as cleaning the bath is concerned or mopping up any spilt water.
The door needs to be moved so it opens against the wall. This gains you circulation space.
I wa going to suggest the whole of the 1500 wall is used for a walk in shower. This should be at least 900 mm wide. I would get a sink about 1000 mm long (we have a shallow trough type one from Duravit with storage under) because this gives a lot of space. On a wall that is 3120 mm long and with the shower taking up 900 mm you still have 2220 mm available! That is easily enough for a very large sink and a loo and leave room for a heated towel rail as you come out of the loo. Put the bath where the basins are in the diagram above. You should have enough room if you move the door. That wall is 1920 mm and that is plenty of room for a bath and a door. You could even have a nice wide bath. This layout means you can clean everything and there is plenty of circulation and you get a luxuriously sized shower in its own enclave! Sorted!
Sink under window is quite normal. Half the bathrooms in the country have a sink under the window. If 740 really is all you have on the door wall then that's not enough for a shower even though you can get the other dimension bigger because you've got the extra space on the adjacent wall. Plus 1500 isn't long enough for a full size bath. So I'd do option 3.
Would something like that work for you/interest you?
One of my friends has an Edwardian house with the bath perpendicular to the window. You would have to move your toilet to achieve that, but I don't know if it's a possibility you have considered/could achieve with your plumbing?