Knitted Yoghurt - alternatives to Yeo Valley Organic Cotswold Wool

[ontheup]

Can you help? I want to make the cushion on p52 of this month's Simply Knitting but dont want to fork out for the fancy dancy organic wool - it says you need 6mm needles and 5.5 mm ones too. The tension is 16sts and 22 rows to measure 4ins square using 5.5mm needles - any ideas?? I'm looking for something quite funky btw. Thanks