I use straight blades to carve with. 1½ to 1¾ inch is my favorite but will go up to 2 inches. Longer than that I don't feel I have control and leverage to the tip. Then try to find the thinnest blade possible that won't be too flexible. The thinner blade will go through wood easier. I like a full flat grind, the secondary bevel will pull the edge off the wood on shaving cuts. Then get something with a decent handle length and thickness so you are comfortable holding it for long periods with out hot spots or hand fatigue.
As mentioned stockman are a good choice because there many sizes and shapes and the blades tend to be thin. Pen knives and congress patterns offer a lot of options. If you can get one or something similar to the GEC 35 Churchill it makes a great EDC plus whittler I love it in that roll. Another option is a Ettrick from A Wright and sons.