How high is the knee wall? You're going to have a window in that knee wall? Dormer or low-set? What is the ceiling height over there? Would a skylight work instead? Why do you prefer not to have the window over sink or shower? I think all of your sketches tend to chop up your space. To have to pass the shower walls on your way to the sink or toilet is rather confining. Usually it's better not to put plumbing in an exterior wall, and it's nearly always cheaper to keep it one wall. My instinct would be to put the sink on the left wall opposite the door, as it the pleasantest part of a bathroom to see when you walk in or the door is left open. Then the toilet next to it. A sink should have 30 inches of wall space and a toilet 32 inches - but I am not sure if that space can overlap in the unoccupied part of the wall - I think it can. And then you are left with the space next to the exterior wall. You could have a big shower the whole width of that wall and a window set high in that wall (or a skylight). Or a smaller shower with the window next to it and shelves or vanity table or chair under the window. You can have frameless glass doors which will keep the visual space open, or even a partial partition and doorless shower - you put the showerhead in the partial partition aimed away from the shower opening. Or you could have a tub with a hand held shower. What you do with that exterior wall depends a lot on your climate, and how high that knee wall is.

What type of window do you have now? Have you thought about converting the window to a transom window above the where the shower / tub would be? That way you could still get a lot of natural light from the window but it would not be in the actual line of the tub.

My question to you is: how much do you like your knees? Love this little conundrum. Reminds me of so many awkward little bathrooms that were made at the turn of the century or earlier, Now I'm not a designer or anything and this is with MS Paint (10 pixels = 1 inch so it should be vaguely to scale I hope) so take this with a grain of salt but: I did move your window but if you don't want to move it you can just flip the position of the toilet/sink (though I believe Door 1 is the kitchen door so I left the toilet closer to the wall bc then it'll be kinda out of view if the door is slightly closed I hope?). Not sure if this would work bc I don't have the dimensions from wall to door trim on Door 2 and I'm assuming its the same size as Door 1 this one moved the window again but kept the same layout you have now. I just sized the fixtures to fit the room; same toilet but adding a shorter than average 30" x 54" 2-sided tub (you could probably get away with 60" length though) and a smaller 18" x 30" sink (and I'd suggest going even smaller with the sink tbh, shallow sinks might help in this bathroom) I went a bit crazy for number 3, no structural changes but a lot of plumbing moves! In this one I would suggest a corner sink if thats still a thing or a shallow sink if you're open to it, they're great space savers! The layout you have now is probably the most efficient one you could have in there with the location of doors and size of the room, unfortunately. My ideas at most have about 19" of walking space between the tightest fixtures granted thats all hip height and below obstructions so it might feel more spacious when walking. I've found with the tiniest bathrooms over the years that vertical obstruction height is the real killer since your arms typically take up a lot more space than your feet! Honestly I'm not sure if this is your main/only bathroom (I think so since you want a tub in a space you know is too small for one) and I'm not sure what things you'd prioritize over others (storage, view, movement, basement access, etc.) or if the non-door/window wall can be bumped out a bit, even partially (I assume not since bumping out that wall is an obvious way to get everything you want) Also on the point of barn/pocket doors: do NOT do it unless you have the money to spring for a top tier one and even then I wouldn't suggest it. Yes, they are space savers but honestly they come with a host of issues (getting stuck (pocket), coming off the track (pocket & barn), cleanliness (pocket), etc) and even then they wouldn't address the issues you have with this bathroom What you really need is to close off or move those doors, even moving the full bathroom to a different room entirely, which unfortunately is not possible. Changing the opening style won't give you more room to put the fixtures you want in there unless you want to crawl/shimmy/sidestep past your toilet/sink which I don't think would be up to code! If after all my rambling you're not into that might I suggest taking a gander at the old Sears (and equivalent) home plan catalogues? They have so many tiny and rather confusingly laid out bathrooms like yours so you might have a moment of inspiration! http://www.searsarchives.com/homes/1908-1914.htm (granted some plans don't show the layout of bathroom fixtures but there are some that do like The Chelsea)

From the drawings, it is unclear whether any of these options can meet code. The minimum clearance in front of a toilet, tub or vanity is 24 inches. A toilet requires 15-inch clear space from the centerline on both sides. The entry door to a room cannot interfere with a shower door, cabinet door, or drawer. It cannot interfere with a person using any bathroom fixture or appliance. The minimum space for a shower opening is 22 inches.