The best luck I've had is to clean with a "Green Machine" or have a professional come in. I use water only with the green machine and am very careful not to get the mattress too wet. Commercial cleaners tend to be very heavy and most often, toxic, so I'd avoid those. For spot cleaning, I've used a weak solution of water and white vinegar, or, for blood stains, hydrogen peroxide. As Joe notes in his response, just be careful not to be too heavy-handed!

You want to be VERY careful proceeding here because you possibly can ruin, cause further damage and void your warranty if not done properly. That said, stains void your warranty, so if not professionally done, you can be out big money. I would recommend calling Stanley Steamer, as they have some eco-friendly non-water based solvents that could work. You NEVER want to use soap and water or household stain removers as it can eat through the plastic fabric, yes, plastic. Most of the major brand mattresses use polyester fabrics that are cheap to produce. Water or sprays will damage the foams. From now on please use a waterproof and breathable protector.