Weaning Toddler

My son is almost 18-months old and nursing twice a day. Once before nap. Once before bed. He eats solids extremely well. He does NOT drink any other beverages except water. He is a solid/healthy weight. I'm 18 weeks pregnant. I'm trying to dry up naturally or just slowly start to cut down the feedings but we have a very strong sleep association going on and I'm a solo mom M-F due to my husbands insane work schedule. If I started to only feed him on one side for nap and the other side for sleep, would that start to decrease my supply? He switches back and forth typically during each nursing session. If I stopped him from that, and only did Left side once a day and Right side once a day, would I start to dry up ? (that's the goal...) Anyone else know of natural techniques to dry up? PS: Please do not try to convince me to keep nursing. There is a long explanation behind why I want to stop and Im definitely doing it....