Here's how I did it :First I wrapped the Feather in dressmaking paper, top and bottom
Then I pulled out a piece of really ugly fabric to make a prototype
I came up with this pattern eventually. I can't make pdf files, so you have to draw your own, with the measurements written on the pattern.
Cut three: one outer fabric, one inner and add 1/4 " seamallowance and one fusible fleece without the seamallowance. The pattern is without seams!!
Iron the fleece on the outer fabric.
Box the corner a tiny bit, 1/4 " is quite enough
Turn, topstitch and you're done!
You can slide it under your machine to use it as a threadcatcher, or to put your gear in, while sewing.
I added some velcro so I can use it with my machine mat . The mat can be used with Sven too and since Sven is a lot heavier and bigger, I can't put the threadcather underneath him, hence the velcro...
Meanwhile I'm very pleased with my sleeve (and myself i might add haha)