In addition to comfort, it's also worth thinking about fueling. On shorter rides you don't need to eat much and you can run a calorie deficit, but that doesn't work on a much longer ride. Especially if you're not good at burning fat reserves, you'll want to keep a steady intake of carbs. Figure out what foods you can digest easily in the saddle and eat pre-emptively (ie before you feel hungry) on your first few long rides. If you want to do really long rides, you might want to do some specific training to improve fat utilization so you don't have to take in carbs at such a high rate, but initially that's your best strategy to avoid bonking.