Their cabin was actually pretty spacious, measuring 9 feet by 18 feet by 8 feet, and it was fitted with instrument panels, guidance systems, a water heater, a toilet and a bunk. Additionally, it was pressurized, so no special oxygen tanks or breathing apparatus were needed. Nonetheless, Piccard and Jones had to both navigate and pilot their craft from a confined space with little sleep. It was really a combination of things. No new technological breakthrough was required, just a handful of small changes and adjustments.
Some good luck helps, but also, very little was left to chance.
Of course, if you leave little to chance, then you're less likely to have bad luck. The other balloon teams realized that they needed to fly in the jet stream in order to conserve fuel. This is why nearly all of the previous flights occurred during the winter season when the jet streams are especially vigorous. The fastest and most reliable winds generally occur above 20,000 feet, and the higher you can fly the more you can conserve fuel, and the longer you can stay aloft. The Orbiter was often flying at altitudes between 30,000 and 37,000 feet.