Holbein Artists Gouache 15ml Primary Magenta

Ngl I'm kinda surprised that W&N wouldn't include a cool red. And that they have a blend for ultramarine and burnt sienna, both typically single pigment paints. If you're looking at gouache only, https://a.co/d/09ELfJhG would be a reasonable option. Edit: for watercolor, here is a reasonably priced single pigment set that is very popular: https://a.co/d/05Ozfudg (it doesn't contain purple, but it looks like a very mixable set)