BM/Formula Intake at 1 year

I know I can switch over to whole milk around the 1 year mark but I'm a little concerned that I shouldn't just yet.  Currently DS is on BM and being supplemented w/ formula.  He, on most occassions will take an 8 ounce bottle and go back to bed in the morning after dropping him off at daycare.  He then wakes up for breakfast, has his cereal which uses about 4-5 ounces of formula.  He eats lunch before naptime, where he takes sips of water from a sippy cup.  My aunt then offers a bottle right before naptime and he generally only drinks an ounce before he's done and doesn't want anymore.  Before bed he's offered the bottle again and he usually only drinks 2-3 ounces.  At his 9 month pedi appt, the pedi wasn't concerned that he was only taking in 24 ounces.  Now at 12 months its down to about 16 oz.  I have no idea if this is normal.  He seems satisfied and has plenty of wet/poopy diapers.  I'm just concerned he's not getting the vitamins/minerals he needs and that I should continue with the formula for a little longer.  Any insights? please share.

Theresa