Paperbackwriter
Most of the brands you are mentioning on here would count as cheap (sorry) and very cheaply made. You really can't expect top quality. I hardly buy any wool items any more but I have several cashmere items that I got from Pure and from Brora a long while ago. Sure they were expensive at the time but they've lasted so well for absolutely ages. Cost per wear is probably less than M&S if you're going to chuck it out after a year.
I endorse this. A good jumper will now cost £100 to £200 and will still bobble; the nature of the beast. I have a few woollies from around 20years ago and the quality was better then. I think quite low grade cashmere. merino or lambswool in now in use.
Can I suggest boiled wool or quilted jackets as an alternative. Just as warm and better for washing and wear.