If it is right by the stove, and you think fire resistant, easily launderable material is a good idea, you could just buy a fire-resistant t-shirt and cut it up to make your own. (If you are in the UK, there's one here for about £20: http://www.ace-safetywear.co.uk/store/click-fire-retardant-protex-t-shirt-s-s-navy.html)

I presume fire-resistant knitting yarn must exist, somewhere, but I've never seen it.