There are two types of toe-clip bindings. In a step-in binding, the skier doesn't have to manually secure the boot in the binding. In a manual binding, the skier must do the securing. The manual binding is better and a little more expensive. Step-in bindings squeak and can freeze up.
Manual bindings are sturdier.
Once the type of ski and the binding are selected, the process of elimination makes finding a boot a relative breeze. Naturally, the boot must fit the binding on the ski. For instance, there are Rottefella NNN I and NNN II bindings. Alpina and Rossignol make boots for the bindings, but NNN I boots don't fit NNN II bindings, and vice versa. The best way to avoid a disaster purchase is to bring the ski and binding and make sure it fits the boot before purchasing the boot.