Previously, I have found three good shops which are located in Pool (near Redruth), Falmouth and Truro.
Knitcraft in Pool has a good selection of wool and is a cozy shop. The lady who works there knits behind the desk. There is a range of pure wools to Acrylics. I bought some nice wool there.
The Wool Basket in Falmouth is a small shop that offers wool, cross stitch and Tapestry. The range of wool is basic from baby type wool to some acrylic bulky. However, they offer Sublime Wool which lives up to its name. I have a jumper made out of Sublime from this shop.
Truro Fabrics in Truro (what a surprise) offers fabrics and wool. It is a large shop and a range of wools from Noro, basic acrylic, Rowan and Sirdar. It is a bit expensive, but you can usually find something to use.
The newest one I have found is House of Bartlett. This shop is in the old guild hall and it is best to phone to see if it is open. The shop is medium size and is stuffed full of wool.
These shops are ones have happened across. I have not ventured to Penzance or up to Bodmin. Therefore, it is not a complete knitting shop review of Cornwall.
Summary: all the people Who run the stores are friendly approachable and quite seriously lovely. I think the best thing in Cornwall is that there are no major department stores, it is all local yarn shops. To be honest I wish them all luck in these hard economic times.
My main criteria institution shop where they sell wool with a decent range and that they can offer advice and have a lovely smile.
We also helped to look after Tino: a Jack Russel datshund cross.