www.kangarookorner.com has adjustable fleece and cotton pouches. The fleece are raved about and the cotton ones not as much though some love them.
There's another too-Chic Papoose maybe? She uses drawstrings I think.
I also have a Mom and Me/Pea in Pod (PIP) hemp cotton adjustable pouch that is wonderful! They are so soft and like a lightweight sweatshirt. This might sound hot but they aren't bad in the warm weather unless it was 90 and humid or something.