Hello.

Here is my solution...
I didn't change the stairs placement in order to save some money for the more important conatraction works.
But in future it semmes to be a good idea to meke a hatch for bacement and folding stairs for the attic. If the stair up will be placed above the bacement stairs it will free some place for another functions, a laundry room for example.
For a wintergarden I sugeest a glass roof and folding door alone with a regular one. So in the sommer period the room can be opened completely to garden. In winter you can use onle a singe door for garden access and keep the heat inside.
Bedroom size allow very easily to place a king size bed, working desk and even to make a small walk-in close (inside a closet is a very buget friendly ikea storage system).
All materials and furniture are sized properly so it's how this solutions are going to look in real life.
The most of the furnitere pieses and some other thinks (bathroom and kithen sinks) are from ikea.
Also there's some DIY furniture pieces: palett plate display, cat sleves made from boxes for storing vegetables.
To bring some more DIY to a regular furniture you can add a porcelein knobs to a regular cabinet furniture. (also from the same https://www.butlers.hu/lakberendezes/kiegeszitok-21/butorgombok/)

Best wishes :)
Daria.