I went through the same thing with my boy. He is 13 months now. He started thinking he wanted to only take 1 nap around 11 months too. Finally, with it being summer, and our other child being in summer camps and such, we were forced to just make 1 nap a day happen for him.
It has worked out fine. He gets up at around 7:30 AM, and he takes 1 nap in the afternoon...So, in the morning we stay super busy, playing outside, going places, etc. We try to do the same in the evening. He naps from about 1-4 PM. One thing that really helps is that he has a set bedtime of 8:30, and has had one since early on. So, when he gets up at 4, we only have about 4 hours to deal with him. :) Also, in the evening bath time is great. It takes up time, and he LOVES the bath. Taking walks in the stroller is great. Anything outside really destracts him. Hope my rambling has helped. :)
The nice thing is, going down to 1 nap gives you a bigger chunk of time to do things as a family. Good luck!