There have been several Houzz stories about tiny houses and the functional items custom built within them. If you search for these stories you will also get names of the companies involved in designing them, and you can go from there....

based on standard sized fixtures there should be enough space for a small corner shower and single vanity with a toilet squeezed into the space next to the shower (which is narrower than ideal for comfortable elbow room) leaving space in the middle to stand and dry yourself or one person to walk behind another... there also needs to be allowance made for the space that will be used by new wall and floor linings so strongly recommend that you research fixtures and collect pamphlets with specifications and consult a plumber before you buy anything but i would prefer a bigger custom sized tiled walk in shower with glass panel and sacrifice a vanity cabinet for a wall hung sink with in wall mirrored wall cabinet and more toilet room for a more spacious feel

Thank you for your rough guestimate, Louise. I will try to get to the cottage on Wednesday to measure and will post them then. Your questions answered: we are renovating to live in it for two years whilst we build our house. Our two sons will visit but probably at different times. I will place a daybed in the lounge in the event that we are all there at the same time. Once our home is built, we will Airbnb this cottage. We are in our 50’s and our intention is to move back into this cottage when the house gets too much for us. So it’s a long term investment with the view of having made the choice of where we would ultimately want to be later on in life - as much as one can make these decisions with all the unknowns. It is very close to a beautiful town - two minutes walking distance to all the amenities. We cannot do extensions as we have an easement and the land is small. As much as we do not want to be ridiculous in terms of costs, we also need to think long term and are therefore prepared to make the changes when our builder strips the cottage. The location will probably support the investment long term. Also to note, my thoughts: We need to add a freestanding gas fireplace into the living room. My thoughts were to place it on the wall that is shared with the kitchen. I intended to remove the wall between the family and dining. This will also allow the northern sun to stream into the living area in winter. The family room would become a dining room/eat-in-kitchen. The dining and living will become the whole living room. The entrance consumes valuable space and I like siriuskey’s idea of adding a powder room there - perhaps with the addition of an extra shower and basin where the linen is and skylights above both rooms for ventilation and light. Moving the front door would be problematic as it would throw off the symmetry and involve changes to the eves.

You will need to use a sliding door. Shower needs to be at least 800 wide. Id have toilet at other end facing shower and run a recessed vanity,with overhang sink, along the wall from shower to the side wall along side the toilet.