Try going to a dealer or used car lot and ask if you can check a car like yours.

You could also add a small amount of fluid such as one cup or so and see what that does to the level and continue doing that until you are near enough to high to make you confident you have enough fluid.

How are you checking the fluid level?

I suggest driving 5 miles or so to get the fluid hot, then put the transmission into every gear for a moment and then check the fluid with the engine idling.

This is how we check the automatic tranny fluid on a fire truck.

There are a couple of you tube videos as well. Wear a glove with something like an old sock on your forearm to keep from getting burnt.