I once rented an apartment that was maybe 200 sq ft, and it had a sliding glass door. Single story. Had a bunk bed with storage under it. Had a combo sink, stove, oven, fridge unit. All very small.
For a bathroom, you put the toilet in the shower stall. Works very well.
The trick is you can't own a bunch of stuff!
Here are some pictures of my tent trailer bathroom. I am not advocating this as a solution, but you might get some space saving ideas. This folds up into a 14' X 7' box. We can live in it for extended periods. We have updated it with 250 watts of solar, 750 amp inverter, 40 gallons of propane, and a 250 aH battery bank. Our only real limiting factor is water and sewage disposal.
At the right in front of the bunk is the shower/toilet which is folded down.
The shower/toilet opens up and includes a mirror.
The shower curtain can stay up when not using the shower, so you can look out the windows, or you can leave it down against the windows, opposite of the door.
It uses a hand held shower that can be secured to the ceiling.
The toilet is ceramic, with a holding tank below it. Very similar to what is used on sailboats. When you take a shower, the curtain just drapes over the toilet. Convenient place to put your soap and shampoo.
Stove, oven, fridge, and forced air heater run on LPG. No insulation in in :( but we camp comfortably in sub freezing temps, just uses a lot of gas.
More pictures here if you are interested.