M0nica
The problem is there is nothing we do in anyway that doesn't present some kind of ethical issue. We just have to balance them all and then decide what aspect is most important to us as individuals.
In this case polluting the ocean v animal cruelty.
By no means all natural fibres are obtained in cruel ways! Mulesing can be cruel, but many producers would dream of using this method of shearing, so it is not a simple choice between one evil and another.
It can be difficult to get information about the provenance of yarn after it has been made into garments, but relatively easy to do so if you knit them yourself. If knitting is not your ‘thing’, though, you can source garments made from ethically produced yarns if you want to.
The chances are, unfortunately, that the cheaper the jumper or the yarn, the more likely it is to have involved cruelty. Buying clothes made from organic fibres, or yarns from small producers is much more likely to be both animal and planet-friendly.