I nursed all my kids well into their 2nd year (stopping between 15-22 months). With all of them, I noticed a big decrease around 9-10 months old, when they didn't need to nurse as much. It wasn't a problem at all. They got plenty of food and milk and thrived. Keep in mind also that their calorie intake naturally decreases around 10-12 months as their incredible growth rate slows down.
I also never pumped. Some women just can't. I successfully breastfed my kiddos but they rarely got pumped breastmilk. My oldest did because I was determined, but even when waking up engorged I'd be lucky to get an ounce or two in 30 minutes of pumping! Once the 2nd and 3rd babies came along I didn't have that kind of time! I say just go ahead and give your baby a bottle of formula (my breastfed kids rejected every kind except GoodStart2, which your son is old enough to have) when you aren't around. Since pumping isn't doing much right now it won't hurt your supply. You can try to pump when you are on your trip and resume nursing when you return.
As for increasing your supply, drink a TON of water. Way more than you think you need. Also watch any meds you might be taking. Almost all cough, cold and allergy medicines are very bad and are a great way to dry up your milk supply quickly (which is why non-nursing women take them to get over milk engorgment issues). When it says a medicine is 'safe' for nursing, it just means it's medically safe. It can still destroy your milk supply and be listed as 'safe' for nursing if there's no medical side effects for the baby.