Hello,
Unfortunately, with laptops, there's only so much you can do to reduce system temperature.
One of them, as you've tried doing, is to use a laptop cooler. Some laptop coolers work better than others, so if you want the best, make sure to look around and check out reviews.
Also, as already said, make sure that your laptop is free of dust. This may require you to open up your laptop. I regularly clean the fan and heatsink inside my laptop to ensure maximum airflow.
Another thing you could is to clean off the thermal interface material between the CPU and GPU and their interfacing heatsinks, and re-paste them with a high performance thermal paste or compound. However, this is tricky and risky since you've got to disassemble and re-assemble your laptop, and there is not guarantee of a significant improvement in temperature.