I love the cover for my tea pot that I made for it. My tea always got cold waiting. I made it with doubled batting and a tiny crazy quilting from left over scraps. One DD loved it so much I let her take it home with her. Gotta make myself another one.
I'd say go look at different tea pots your friends have, or are sold in stores near you. Measure them with your hands, easier to explain to clerks!! Mine was more or less a rectangle one, and with left over batting that I sewed together by hand. I don't like to throw anything away.
If you have a Civil War Re-inactment held somewhere near you, or a group of them near, then apron and sun bonnets are good sellers. I took apart my own Grandma's old sun bonnet and made a sister and daughter copies. Used tiny flowers in a dark field and bleached them. For the other one I got a big old dress from a church sale and it looked old. Both said women tried to buy them as they wore them at the re-inactments. The aprons can be either waist tied or neck ones, but should match the bonnets. Grandma's bonnet brim was stiffened with card board, but I used slices from bleach jugs so I could sew them in permanently.