For the bathtub, I would recommand a two-part epoxy bathtub paint. This type of paint can be used on porcelain, ceramic and fibreglass.
For more information, I would suggest this article: https://renoquotes.com/en/how-to-remodel-bathroom-using-paint
Although I think it already look pretty nice, I also think that the tiles are a little bit too dark and too small for such a tiny space. With a bigger tile and a brighter color, the bathroom will instantly look more spacious.