I have several balls of worsted yarn in my stash and a pair of 15 mm needles - size 19 in American-speak, I believe. Can anyone tell me how many strands of this yarn could be used together with this size of needle? One of the things I was thinking of doing with it was making a blanket.
It's going to take 2-3 strands of yarn which may use up your stash pretty quickly. Try a swatch with 2 strands and see if you like the look and feel of the knitted fabric. If not, add in a 3rd strand and see what you think. You could also mix different yarns and weights to see what works best.
You can use 2 or 3 strands, why don't you make a sample first using 2, knit for several rows, then add another one and work with that, see which one you like.