Here are a few suggestions, to get you started:
Before you go and buy something, check out your closet, there might be some forgotten
pieces that you can give a second life to. If there's nothing to work with there, then:
Visit your local craft store for 100% recyclable polyester felt.
Cork leather: The Little British Fabric Shop
Wool felt: Filzfelt
Miscellaneous sustainable fabrics: Pure Fabricz & Offset Warehouse
For a wider list of online shops that sell sustainable materials you can check out Refinity