I would do something like 4h A, long nap 1.5-2h, 4h A, 30 min CN, 2-2.5h A. Worked fine for us at this age.
If the day getting pushed forwards is an issue, wake him in the morning at 7 instead of waiting for him to wake. Or cut the CN even shorter than 30 mins to make sure he'll still go down at BT.
The alternative option is to start cutting your morning nap shorter and aim for a long pm nap which works for lots of Mums. Take a look at the FAQs about the 2-1 transition for some more information
