Cashmere combs like this one (available from Amazon and elsewhere) are gentler on woollens than batter operated shavers. They only work on natural fibres though.
I think woollens are one of those items on which it is worth spending more to get quality. Natural fibres look better and wear better, are less 'sweaty' and don't need washing as often as manmade ones. You should air wool jumpers more often than you wash them. Not only that, but there are grades of yarn. One ball or garment in 100% wool (or cashmere or alpaca etc) is not necessarily as good as another, and generally speaking you do get what you pay for.
A good jumper should last and look good for years (if you can keep the pesky moths off it and are willing to hand wash it and dry it flat
). They can be expensive, but it's like the Vimes boots principle - if you can afford a good one it will work out cheaper than having to buy several cheap ones.