RUn your plastic plants over a pair of pantyhose. if they don't snag or tear, it should be safe for your betta. If you do buy decorations and you feel they're sharp, you could always sand down the pointy parts.
Thanks for the advice everyone! I bought a thermometer last night just havent put it in yet. ;) And he is building a bubble nest right now! It's really neat watching him make it. He just keeps going up for air and moving to the side to make the bubbles go where he wants them. So cute!
you can always put the bubblenest in a little cup of water and cahnge the rest of the water.... It works ok... not the best, but thats what I like to do if my little guys seem really proud of their bubblenests! lol