Another idea. Take whatever you choose (ie. perfect push up, books, chairs, medicine balls, etc) and now wrap a band around your back to use as resistance. They are cheap and take up almost no space. Iron Woody is a good place to order from and they come in varying resistance levels. I would wait to use the bands until you are comfortable with whatever unstable surface you are using. Additionaly, you can add bands to just about any exercise you choose in the weight room. I trained with bands while deployed last year and had great results.
I couldnt find a video of band push ups, but there is one of Band DB Bench. Placing the band under the arm pits is best. See the videos and websites below.
DB Band Push Up
http://www.xlathlete.com/view_exerci...xercise_id=332
Iron Woody Bands
http://ironwoodyfitness.com/fitness-bands.php
If anyone wants anymore info on training with the bands, just PM me.
Milon