there are a number of brands, types, weights...i love using perle cotton -- usually for wool applique- and for crazy quilt embellishing-
i love the newer verigated balls of perle cotton our lqs is carrying- i've used DMC perle cottons for years- many many colors---
weights are something like #3(very thick) #5, #9- i don't know if there is a thinner one than #9- in my collection i have all #5 & #9
you need a larger eye needle- other than that- its like using embroidery thread you do not have to separate.