Your bedroom door is 180mm wide, so make it 180mm!
The threshold is a stone threshold-a stone slab that solves the height difference between inside and outside, solves the transition between two materials, blocks water and plays an aesthetic role. Due to different material practices in different rooms and different floor thicknesses, the height difference is caused, and some materials are not easy to "collect".
For example, the indoor floor of the living room or walkway is paved with laminated wood floors, the thickness of which is about 12~ 15 (8 thick floors +5 thick mats), while the bathroom floor is tiled, including the thickness of cement mortar+the thickness of tiles+the thickness of ground water slope.