Since you asked, Donna Lee, the striped tea cosy is done in a slip stitch pattern I improvised, worked over a multiple of 4 plus 3 stitches (keeping in mind this is worked flat, not in the round):
(after a few set-up rows)
2. Change colour: (K3, sl1) repeat to last 3 sts, K3
The wool was 8 ply, the needles 4.5mm - though I think I would have preferred 4mm.
The base curls up, and if I did it again I would start with some ribbing to avoid that, which would also draw it in around the bottom of the teapot a bit.
I tapered the pieces at the top, and put in a row of eyelets before casting off. It's made as two flat pieces which are sewn together just at the top and bottom, leaving space for the handle and spout.