As an alternative to conventional carpet, consider sisal, jute or seagrass. Sisal flooring is made of fibre taken from the agave plant, grown without using pesticides or chemical fertilisers. Crucial Trading offers it in a range of colours.

Also worth a look:
www.thenaturalfloorcompany.com
www.alternative-flooring.co.uk
www.kersaintcobb.co.uk