D.K.
Hi L., I can sympathize. This reduction in supply is normal, and is concurrent with his decreased need of it.
I continued at least one nursing session a day with my older son until he was 2 1/2. It's a very special time of day for both mom and baby. I was in the military so I was at least full time at work. By your son's age, my son was no longer taking the day time bottles, but we nursed when I got home. At this age and beyond it's primarily a comfort thing, so if he wants to nurse, let him, but he's not nutritionally dependent on it any more. Just make sure he's getting whole cows milk regularly through the day and a balanced diet of table foods. He's ready for it. You don't have to give up nursing altogether. Even one session at bedtime will maintain that special bond.
Bottom line is, you shouldn't worry about decreased supply since he's ready for cows milk (whole fat of course). You can still provide that comfort but don't worry he's not getting what he needs. Table foods are sufficient at this age.