You need Jersey or interlock (can also be labelled as single/double knit) either all cotton or about 98% cotton with spandex/lycra. 5m is safe and you can cut it down the length, (and gift the other part as another wrap if you like).
I found the fabric for mine on a sale table for a few $ a m so it was a bargain. but bear in mind you can get a sleepy wrap for $60 new or $30ish pre loved though.
You are probably going to find a stretchy hot though as you do need 3 layers over baby to be safe.
The other option is a cotton with good diagonal give, like a quality gauze, but that will need hemming.