Have you ever tried Bio-Catolet? It's different from the clay type, but we use it and far prefer it. If you haven't seen it, it's basically clumps of recycled paper. A LOT less messy than clay, and, in my experience anyway, works better too. Never seem to get any smells, an its also biodegradable. The clumps are much larger than the clay type, so you'd have to change to it gradually (mixing the two in for a while), but i'd recommend it. You can buy it from most pet shops, and also in supermarkets - I think Tesco and Sainsbury's both stock it.