If you really insist on live plants, my thought would be to give it normal bedding (Ex: Aspen, Cypress, Towels) and pot the plants. A great plant that I have used for other herps is pothos, though I have never used it with a BP The soil would be a bad idea, because if you are using belly heat (which you should always use a thermostat for) the heat would become trapped, and build up dangerously hot pockets.

I can tell you are concerned about the decor and everything, but the most important part is getting proper temperatures and humidity. What are you using as the enclosure, and how are you planning on heating it? Remember, you want a hot side basking spot (surface temp.) of about 90 degrees, and an ambient temp(the air in the enclosure)at about 80. Do you have a digital thermometer? It is critical to your success in this setup. if you do not, you can get one for pretty cheap at walmart, it is called an an accurite thermometer-hygrometer, and it will measure all of the temps you need. Sorry for the monster post, and good luck with your snake!