Even with proper saddle height, you should be able to stay on the saddle when coming to a stop, and lean to one side and still get a toe down. I often do this while keeping the foot of the dominant leg on the pedal ready to push off from.

(don't try with clippless pedals/road biking shoes, as you will damage the cleats and possibly slip - in that case, get off the saddle and get a heel down).

If you feel unsteady with only a toe down, apply the brakes while stopped. This will prevent the bike from feeling like it will get away from you, and will allow you to put a little more weight on that upward facing pedal without actually moving forward. This in turn will in turn help you with balance and with pushing off once it's time to go.

I don't advocate stopping on a curb to get the whole foot down, because you won't always have a curb. Ultimately you need to get used to stopping anywhere at a moment's notice. Anyway, once you get used to stopping without a curb, stopping by putting a foot on a curb will likely feel really awkward (at least it does for me).