Tea cozy questions

I would like to make tea cozies for a couple of friends. What type is best? I see that there are two major types, one that fit on the teapot and one that goes over the teapot. I know wool is the most insulating but should I use superwash or would a wool blend work?

I think the kind that goes over the teapot is easier to use. Superwash or a mix would be good.

For one that fits on the teapot, you’d have to know what shape teapot they have. You wouldn’t want to make a cozy for a short fat pot only to find out they have a tall slender pot. Plus where the spout is - I’ve seen round ball shaped teapots with the spuout starting low near the base and others where it’s up high.