I have had good success with Arches Hot-Pressed Watercolor, may be called Aquarelle in some markets, comes in various weights. I have tried the 90 and 140 lb weights, and like the 140 a bit better. It has a natural creamy surface, great wet strength. I use it where Platine may be too white.

For cyanotypes, I like BFK Rives White, the paper is about 90 lb, giving a good color, and clears easily.