How to Determine Meditation Object

I have practised previously with the breath, but I feel my eyes fall automatically when setting attention on the breath, and inversely, focusing on objects makes my mind alert. Is this sufficient to switch meditation object? **Q1: What are the best ways, or the best way, to determine proper meditation objects?** **Q2 : Is there any real drawbacks of meditation with a physical object or mental image as compared to the breath?**