Hello Malcolm
Since we specialise in cane & rush seating, and the supply of materials for DIY projects, I'm probably as well qualified as anyone to reply to your query.
I'm surprised to hear your local caners aren't used to large caning jobs though! I'll tackle anything, though of course the bigger it gets, the more it costs. Whether it's worthwhile is really up to you: it depends on what sort of value you, personally, would put on the chair. Central heating in itself shouldn't do too much harm: I find the worst damage seems to come from leaving chairs in direct sunlight, rather than just dry heat. You can always spray the back of the canework with water now and again, anyway, if you're worried.
Is it vital to recane the chair in exactly the same sizes as the original? We can certainly obtain the more unusual sizes if you require them, but generally we just use the nearest commonly available size, as these others have to be ordered specially and therefore cost more.
Do I understand that on the back of the chair the holes finish off in a groove, which was originally filled in with a narrow strip of wood, and this is now missing? We do come across chairs such as this from time to time, and you really need a woodworker or furniture restorer to make a new strip of wood after the caning is completed, as it has to be almost invisible after sanding and polishing.
If you'd like any more information please email me, but take the dog out first.
ally