I have a 10 month old and sail a Bristol 35.5 on the Chesapeake. We bought an extra pack n play to keep on the boat. It is very convenient as he can take a nap in there and sleeps pretty well, or we can put him in there with a few toys for a bit if we need some extra hands. Our cabin sole is pretty opened, so we have actually fit two pack nad plays down there at once. As far as a berth with a lee cloth, we have not tried that yet.
I highly recommend the Jim Bouy child safety harness. It is $29 and can fit an infant. It takes some time to get the size right, and you might want to cut the excess straps and then burn the ends. It comes with a tether and everything. The reason why we like this is because his PFD is very uncomfortable and he is not mobile at all. , He has that harness on any time he is above deck. Now that we have the harness, he wears the PFD going on and off the boat and in the dingy. Before we had the harness, he would only last 10 minutes or so before getting really fussy in the PFD.