Here is my tutorial for the welly warmers. It probably isn't the "best" way of making them but it is a quick and easy way of doing it.
1 - First draw around your welly. When you draw around the sole keep the pencil flat against the welly so the nib ins't against the sole, this gives a bit of wriggle room (hopefully that makes sense if not I will take a picture of what I mean)
2 - Once you have drawn around the welly add 1/4" seam allowance all the way around it. Do not add the seam allowance to the sole. Once cut out the sole should be the same size as the bottom of the welly without the seam allowance.
3- Pin the pattern to the fabric and cut out. You need 4 pieces of the boot shape and 2 soles. If you are using patterned fleece you want the right sides together as that is what you will see in the welly. You want the stretch of the fleece to do the width of the boot and along the sole.
4 - Sew a 1/4" seam down the front and back of the boot shape (or you can use an overlocker)
5 - Pin the soles to the boot shapes. Be careful as the soles will be shaped for each foot so there will be one left one and one right one. I fold the soles in half length ways to find the middle point which is then pinned to the seams and then continue to pin all the way round. Sew with a 1/4" seam or overlock.
6 - To make the top band I copied the top part of the boot pattern (2 1/2") and doubled it. The sides do not have to be slanted as in my picture, it will work if they are straight as well. Pin to fabric (with the stretch along the width again) Cut out 4 pieces.
7 - Sew 1/4" seam (or overlock) right sides together. Once sewn fold over so the seams are enclosed.
8 - Pin to the inside of the boot shape raw edges together. The seams should be on the outside of the boot shape, you do not turn them. Sew round, repeat with other boot.
9 - Finished! The Welly warmers are now ready to go in the wellies. The seams stay on the outside so the don't rub against your feet and the top band folds over the top of the boot to stop them from rolling down. It does make your wellies a bit tighter but it should also keep you feet warm!
I hope this tutorial is helpful, any questions or problems just let me know in the comments!