I couldn't tell from your post when your ds goes down for naps, but my dd has a snack right before nap, to tide her over so that she can have a decent sleep. We introduced that at 8 months, which is when her milk feeds stopped being exactly four hours apart and became more in line with regular breakfast, lunch, dinner, and bedtime snack times.
Here's our basic schedule:
8:00 - breastfeed
9:00 - solids
10:45 - snack
11:00 - nap
12:15 - breastfeed
1:15 - solids
3:15 - snack
3:30 - nap
5:30 - breastfeed
6:30 - solids
8:15 - breastfeed
8:30 bed
However, she's on the small side (17 lb at 9 mos) but eats a lot, so it may be easier for her to last that long between feeds.