It's finished and I'm wearing it now. It's lovely, soft and cosy...
and it fits!
The pattern (Chevron Lace Cardigan by milobo) is available free on Ravelry here. I followed the 42" pattern size and used a 9mm hook for the chain and first row (and also for the chain under the arms) then a 6mm hook for the rest.
The wool was another Kemps wool bargain. It's Wendy Merino Bliss and was £2.30 per 50g ball. They don't have the green available any more but there is a lovely purple on offer (it was a hard choice between green & purple for me). I used 8 x 50g balls.
I'm quite a novice crocheter and I found it relatively easy to do. It's a bit tricky getting started (as most things are) and you've to watch out for row 5 (the pattern changes slightly and is easily missed), and I had to fiddle the sleeves a little but noone will ever notice that unless they want to examine my armpits very closely.
I would like to make another one without sleeves (which would take 6 x 50g balls for my size), I've already seen wool I like...