Making sourdough bread in a warm and humid climate
If your starter is tripling in 3 hours, it's unlikely that you need to add additional yeast.

If the humidity is causing your dough to spread as it rises, you could try slightly lowering your hydration to account for moisture in the air. You could also add a fold in your bulk ferment time to give more gluten strength.

You don't mention how long you are proofing your loaves, which could be very important. Generally sourdough will need several hours at a moderate temperature to rise properly. Be sure you aren't rushing to the oven. (When you poke a loaf, it will gently and slowly spring back when it's ready.) This may mean that you will need to proof in the refrigerator, basement, etc to keep your loaves cool as they proof.

Finally, if spreading continues to be a problem, adding some vitamin C powder (ascorbic acid) can help get more volume in your loaves. This works by making the gluten tighter, so use it sparingly. It is especially beneficial in whole grain sourdoughs.