Because your slab is suspended above a basement, you could float a plywood subfloor or adhere a subfloor to the slab. When we float a subfloor, it is usually two 1/2" or 5/8" plywood layers installed on a diagonal layout to the room with each layer staggered so no seams line up. The layers are attached to each other only. The plywood needs to be dry and reasonably flat. Garbage sheathing will not suffice. Since yours is such a large space, I would suggest you do a lot of research on different install options and consult with installers who have done solid over concrete slabs. One important thing to note is the fact that even though your slab is suspended construction does not mean it is entirely safe to assume it is dry enough to install wood flooring over without providing for some sort of moisture barrier or retarder. Concrete can take up moisture and emit moisture depending upon the temperature and moisture vapor content in surrounding air at any given time period. There have been remarkable advancements in adhesive technology with some adhesive manufacturers making the claim that now you can install a solid to concrete directly when using their product designed to do just that. I have not done that. Engineered wood flooring construction is basically a quality plywood with a veneer face that is the specie of choice. The veneers differ from product to product; some have a thin peeled veneer and others have a sliced (sawn) veneer. The unfinished Owens engineered is of the sawn type with a veneer that is almost a full 1/4" thick. I did an Owens unfinished over sheet cork over a slab where the product married to an existing 3/4" solid wood floor attached over a portion of the house that had a basement. You could not tell the solid from the engineered. Good luck with your searches.

I like my first idea best as far as use of space. I know people say not to put toilets on an outside wall. We had one in our last house in Iowa, but we had 2X6 construction. I don't know how high your window is, but I'm guessing the toilet would fit under there. The shower would be 5 feet long or shorter if you want a wider space to get to the toilet. (kind of tight the way I have drawn). You could do a 5 and half foot long shower and do an angled door at the left end to allow room between the shower and toilet. The vanity would be about 7 feet long, unless you do a 60 inch vanity with a linen cabinet at the door. I would reverse entry door swing if you do that.. The second top right could work and you would still have a small closet. The bottom left plan would require waterproofing your front window. Hopefully someone will give you other ideas. The bottom right plan is bigger, but no closet. Each square equals 1 foot.

what a beautiful room to start with. and the colors you have chosen are very calming. as a guest room or air b&b the first change I would make is to get nights stands and lamps. something for BOTH sides of the bed and move the tall dresser by the bed out of the room. everyone needs a place to put drinks, glasses or books when its time for bed but most people don't unpack a suitcase for just a few days. which also means there should be something to put that suitcase on. I'm thinking between the 2 windows would work. a chair in the corner by the fireplace and windows would be nice. normally I would say NO TV in the bedroom but if you are planning on renting the room out you should have one that would hide in the unit next to the fireplace. replace the generic overhead lighting to something nicer and more interesting. blackout curtains a must but have them completely open past the window to give the most light and view when the are open. 2 smaller 3X5 rugs or a runner either side of the bed would be cheaper than a large rug that is mostly hidden by the bed itself.

I am also always drawn to this inspiration pic of jute/sisal look with light gray walls too, but my husband likes gray as he thinks it won’t show as much dirt and wear....