Sorry chaps, I should have clarified
Two handed, two colours, purling I can do. So fair isle if you swap colours every one or two stitches is fine. But Philosophers wool shows you stitches 3 and 4, for when you are doing more like intarsia. So you can carry your colour across, weaving it as you go, with no floats.
But I tried the 'pretend to knit, pretend to knit, un-pretend, bring it through' part of stitch 4 with purling and seemed to get in a tangle
So its philosophers wool stitches 3 and 4, purling, that I'm after please clever peeps.