Proper Meditation Upon A Physical Object
I cannot answer your original question, however, I second the comments above: stick to the breaths.

I would recommend using Buddhadasa Bhikkhu interpretation of the scriptures for the 1st step of your meditation: learn the long breath by controlling the flow of air coming in and out of your lungs, this will relax your body and help you move to the next steps.

Much more details here:


Mindfulness with breathing: Dhamma Talks
Mindfulness with breathing: full book