Look at this video about Shalina in Sacramento and her tiny house on wheels. She built it for her and her 15 year old daughter. There's a lot I like about it. She put the two bedrooms at different ends of the house so there are separate and private spaces for both of them. She also made a lot of clever storage solutions, for instance one in the kitchen ceiling. There's a lot of white, which I appreciate. The dark wooden floors and ceiling looks nice, but I would go for lighter colors to get the light reflected into every corner as much as possible.
The only thing I didn't like was the plot they put the house on. It looks like a trailer park. I would like a much larger garden. When you live small, the outside area and surroundings are more important.
The cost for the whole build was around 35,000 USD. She did it all herself and saved a lot that way, but it sounds like a very good price for what she has. The total area is 32 ㎡.