I highly recommend using Malabrigo Worsted; it felts more than many other worsted yarns.
Malabrigo Yarn, Merino Worsted (100% Merino
wool, 210 yds/100g)
C1: Azul Bolita, 2 skeins
C2: Lettuce, 3 skeins
This was a successful experiment. I like welts so much, I decided to see what happened when I felted them. It created a really interesting texture. These booties remind me of the clown booties, but in a good way.